I'm 6'2, 240 lbs and I also sometimes wish I'd gone extended, mostly to get my head and helmet under the halo of my track frame.I went with the track because I like the look and added protection. I wont admit it too much but wish at times I had the extended due to the space behind the seat. The mounts have 3 positions for the seats but if you are really short I would suggest sliders.
I'm very happy with the track frame, even if it is a little more awkward to get into, because when you start driving fast the holy shit factor is more fun being surrounded by a metal frame.
I've trying to figure out aftermarket seat and welding new mounts to get my butt as low as possible but I'm not sure I'll actually be able to get low enough. If I'd gone extended, I've have 2 inches more height, and I could get reclining seats to lay down more. I'd say if you're like 5'10 or more and plan on wearing a helmet you might want the extended frame.