I recently built a character specifically for farming the ledge on merciless. Interested in sharing, as well as any opinions on how to tweak/improve it.
Pure Merciless Ledge Farming Ranger
I'm currently at level 53, will eventually level to 55. Merciless Ledge is Monster Level 53, so character level 55 is the cap before item drop penalties kick in. My Life is 839, Energy Shield is 29, and I have no mana.
Skills
I need to use 2 5-links for my 2 attack options. My bow is Lightning Arrow + Lesser Multiple Projectiles + Chain + Life on Hit + Increased Item Quantity. My chest is Elemental Hit + Faster Attacks + Life Gain on Hit + Increased Item Quantity + Increased Item Rarity.
I use Lightning Arrow to clear mobs and Elemental Hit to clear magic and rare monsters. It's better to kill whenever possible with Elemental Hit since I get the buff for Increased Item Rarity that way, but when I'm dealing with big mobs of white monsters, the clear speed of Lightning Arrow more than makes up for the loss of IIR. Life on Hit is necessary on all attacks to keep the character firing and alive. Life leech takes time, while Life on Hit is instantaneous. I need instantaneous life regen for all of my attacks or I'll die within 2 seconds.
I use the Projectile Weakness curse sometimes, mostly on magic and rare monsters. I should probably link it with faster casting but I haven't done that yet.
I don't run any auras since my life is very low and haste or damage auras would drop me into the realm of getting one-shotted too often.
Magic Find
Current magic find gear is pretty mediocre: perandus belt (9% IIQ) and goldwyrm boots (27% IIQ) are probably about as good as I'll get and I have a hat with 14% IIQ + 29% IIR that will be hard to upgrade. I have a good pair of rare boots with 16% IIR, 16% IIQ, and 30% movement bonus that I may end up using in place of goldwyrm. I have pretty bad IIQ+IIR rings and would prefer to swap in a couple of Andvarius rings if I could get my hands on them. Also should swap my terrible gloves for Aursieze if I could find some of those.
With better gear, I'll probably be looking at approx. +125 IIQ and approx. +150 IIR (Lightning Arrow) / +200 IIR (Elemental Hit). I'm focused a little more on IIQ at the moment but every upgrade I'd get would be lots of IIR at the expense of a little IIQ.
Passives
Here's my Passives Tree: 
http://www.pathofexile.com/passive-skill-tree/AAAAAgIAAdEFLQ6tEC0UdRXwFx0Y2xm0Gf4a2xsBIWAotSmlLOkyCTWSOlJAoEOcSn1OyFYEVvpgiGFSY6dnoHRBdPF464Zgh3aNfpstnrmfy6GkokCr0q_rt7a-p8APwdjEosrTzZjSTdN-3BXcgt0N3Ubext-_5wrqYu4O707vevT4-WP6sfxO_MU=
The goal here is to collect as many attack speed + bow damage + movement speed nodes as I can and forego survivability. Unwavering Stance + Iron Reflexes is necessary to prevent getting constantly stunned, since this is a low-life character build. I use blood magic combined with life on hit which works very well to keep me alive and shooting. I picked up a few life nodes and diamond skin just because the character is such a glass cannon that I need a little bit of leeway when dealing with rare monsters. I need some life to keep me from getting one-shotted when I don't want to die.
I will respec out of Golem's blood when I've completed the build, but it has been helpful for levelling just because without it I had zero life regen and had to keep guzzling life flasks.
I have the potential to get 5 additional Quest Reward Passive Points (way forward, bandits, sewer busts, kill piety), although I'd need some kind soul to more or less lug my character along to get most of them. I'll also get 2 more passives for levelling. The reason I haven't levelled to 55 yet is that I figure that if someone is willing to lug me around to do stuff like kill piety in A3/merc, I may accidentally level once and I don't want that accidental level to put me at 56 and into the item drop penalty.
I'm not yet sure what other passives to take to finish this build. My options:
Savant: I need more Int. to level up my IIR gem. Savant gives me one more level, or +2%. I probably have to take this one.
Greater Impact: It costs 2 points, I get a good damage buff. Also probably makes sense to take this.
Increased Movement Speed: I can take up to 3 of these at 3% each.
Heartseeker: Costs 3 points for increased crit
Master Fletcher: There are some assorted bow damage/accuracy/crit nodes I can access immediately as well, up to 5. Master Fletcher itself costs 3.
Flasks
2 +20% Quicksilvers with Adrenaline Suffix
3 +20% Seething Hallowed Life Flasks (Panicked OK too, maybe better although it doesn't really matter)
Gameplay
As soon as I hit the ledge waypoint, Quicksilver to the first mod and spam lightning arrows. Magic and Rare monsters get cursed with Projectile Weakness and then I use Elemental Hit. Pick off stragglers with Elemental Hit as well, if I'm feeling like it. 2 +20% quicksilver flasks is enough to sustain constant sprinting between mobs. When I get to that big lightning totem, run right next to it and let it kill me. Respawn in town, sell my rare items, stash good items and currency, and reset the ledge instance from the town waypoint. Basically, dying is my town portal.
Life on hit keeps me at almost full life all the time, although i will sometimes get pretty low on life and i just have to drink life potions fast. My life pool yoyos wildly from full to 20% to back to full when i fire a volley of lightning arrows into a mob.
It's also necessary to die a lot to keep from levelling. It's bad to die in the middle of killing mobs/rares since I want to collect the loot. It's annoying to kill a mob that drops a chaos orb 3/4 of the way up the ledge, then die before I can pick it up. The best way to deal with all of this is to be able to withstand one or two hits from a rare monster and plan to just die at the boss. Fortunately, because of this character's terrible survivability, I die a lot.
Strength of the Build
Unlike Merveil farming, I get plenty of scrolls so this sort of farming is completely self-sustaining. There's also almost no wasted time since I never have to run through content I don't care about to get to something I do. Spawning right next to Nessa after I die is also better than popping portals since it takes less time to run to her and sell the rares I collect. I routinely get a whole screen full of drops and it takes me a few seconds to actually sort through it all. Also, it seems like it's considerably easier to get 6-slots and 5-links this way, although I don't really do a lot of Merveil runs (I really, really hate running that cave) so I can't confirm.
Anyways, this is the first character I've built from scratch without any sort of guidelines, so I figured I'd post it to see if people think it's any good.