Forged Pistons & rods, between 9:1 and 10:1 will handle 400 whp. Possibly even more, if the tuner is good. If you go any lower, your car will be too slow until boost kicks in. Will really suck before you get your turbo.

I'd say go for 9.5:1 CP pistons. You won't sacrifice any noticeable power before you get your turbo kit on.