Re: Pistons 9:5 Compression
I agree with chinke, if you're going to stay with Stillen, I'd go with stock compression. There are much more heavy duty pistons available, and you don't need to drop the compression ratio for Stillen's boost/power levels. Another big worry is the rods, and you should, at a minimum, go with Eagle H-Beam (relatively inexpensive, but MUCH stronger than the OEM rods).
Also, I really haven't seen 9.5:1 CR pistons available. The closest you can get is 9.0:1, which is what myself and chinke both have... 8.5 would be way overkill for the Stillen.
So my $0.02 would be to go with 9.0:1 pistons if you think you have possible future plans, and just stock compression pistons if you plan on staying with the Stillen. Look into Arias pistons, they have a good record in the 350Z community, and I'd recommend having the .020 over-bore version as you get a fresh cylinder wall honed to fit each individual piston to keep from any slop from tolerance issues.