For someone who likes to play a lot of high gain leads (Think Petrucci), what would be a good humbucker for the neck position? I'm getting a GFS prewired with a humbucker in the bridge and would just like to replace the single in the neck.

That is, of course, unless the single coils are fine for high gain in which case, we're all good here. ANybody have experience with these?
Well the single coil would probably give off some noise when using high gain. Maybe look into these http://www.guitarfetish.com/Black-NEO7-Neodymium-Single-Pickup-Hotter-than-Vintage_p_122.html
If you do not absolutely have to have a single coil though then maybe look into a single sized humbucker like the lil killers.
If you're looking for a Petrucci-esque tone, then you want to avoid single coils since they aren't as smooth as humbuckers. My advice is to listen to demos of several of their humbuckers on Youtube. I believe he uses a hotter PAF style of pickup, so you may start there. Maybe look at the Fat Pat?