There may be something to this running fast thing. Went out last night, and was supposed to be 4x1600 race pace. My neighborhood is tough to lay out a run like this with all the hills, and I don't have a track close enough to run to. So I just figured I would run 4 miles at my target race pace.
At mile 3, the first bolt of lightning started overhead, so I turned toward home. Ended up at 3.81, mainly because the lightning and thunder were directly overhead, and I don't play the lightning game, even for .2 of a mile. (plus I was at my front yard).
Anywhoo, pace time was 8:14.

HR 167. I actually think I may have more to give here, if indeed I need to be in the 170's on race day.
The funny thing is, as I'm starting to run these faster runs, I'll start slowing a bit, and look at my HR monitor and see I'm at 168, and tell myself: "You got this. You are trained to be in this zone. Keep going you pus.s.y" And it works.