ok if you are sure on sticking with the stillen then i would go with 11:1 so you won't lose any power since getting more air out of that charger is going to be hard. If you call voretch and do a core exchange on a V7 it will be a toss up between the 10:1 and 11:1 pistons. you lose horsepower every time you go down in compression ratio, but you lower cylinder pressure, so unless you can boost the engine more to make the power back(and then some) sticking with stronger pistons and the factory ratio is the way to go. This is especially important when dealing with an undersized blower because it can only push so much air. with the v7 you would be able to make up for going down to 10:1. I believe the v7 also has the larger higher speed bearings in it so it can be spun much faster, but is externally oiled so you would either need a pump and reservoir setup for it or tie it in to the engines oil circuit. the v7's compressor cover is a bit larger as well so no guaranty that it will fit without a little work. once you get to that size tho you are going to need additional cooling by the way of meth or redoing the intercooler piping. also if you havent relocated the MAF sensors already you should do that. the inlet pipe on the stillen kit is also very restrictive with the offset coupler going to a single 2.5" pipe(
stillen that is HALF of what the car had stock to breath through)
so to sum it up
if stillen v3: 11:1
if stillen v7 +upgrades: 10:1
or just go 10:1 sell your kit go turbo and you will have 600hp.
Also if you stick with it and have the piping re done the stillen intake manifold is garbage and should be used as boat anchor like it was designed, if you can use the factory manifold and an air to air inter cooler I guarantee you will gain power