The free crap is what bogs you down with these "deals." Anti-virus programs are most likely necessary but all are not what they seem. Some, like McAfee, dedicate a lot of RAM/CPU while running in their default modes. If you don't want to build your own PC (and I highly recommend it, its not very difficult at all - put thingy into the spot it fits in type easy), I'd advise you to look into gaming PCs specifically. Most of those skip the junk programs and give you a PC that will game at a decent level and not give you the buyer's remorse of purchasing a Dell.
Look into building your own PC. It's not that difficult to do and your user experience will be far superior with the caveat being that your components work well together (very simple research). Manufacturers will give you detailed information on which components work with other components. Since you are look at a mid-range gaming PC, their specs should be very detailed and accurate by now. It's the higher end builds that get wonky when it comes to what's going to work with X component.
Also, you want solid state drives. Period. The time that it takes to retrieve and write information is more important now than CPU/RAM speed. Games tend to be 10, 15, 20+ GB now. Accessing that information as quickly as possible is key to a speedy computer.