The length you want will depend on who's studs you're going to use. I had the 0.92" track on my sled, and used 1" studs. They stuck up just over 1/4" ABOVE the track lugs. The shop I bought my studs from messed up and gave me 1.075" studs, and they were too long. I put a couple in just to make sure, and they were easily 1/2" taller than the track lugs.
If you get them too long, you'll have that much more chance for tear-outs and bent studs. Go with what the stud manufacturer recommends. I ran 192 Woody's in my sled (using their recommendations for length, number, and pattern), and didn't have any problems for the 5 years I had them in. I also used the steel backers.