I assume we are talking just stock shortblock with a modified top end?
I keep hearing people say just go for it, but I think some are forgetting the weaker link parts he has.
It should be about the purpose of the car, what the driver wants, and how much extra money/time the owner has if something was to go wrong.
Safety is in the tune as far as detonation goes, but that doesn't mean catastrophic failure isn't around the corner with a safe tune. We all have heard about guys taking the T5 down the strip 200 times with 500 whp/wtq, but how realistic and reliable is that compared to those who didn't make it that far?
I still say it like this. OP, if you can afford to have it break down both financially and as transportation, I say go crazy with it. If you can build it back stronger and just want to have some fun, do it. If you need this car to be running for a while or you can't afford to not have the car running, you probably should stick to the 9psi pulley.
I know some of you don't think it's that big of a deal, but the more power we make the more likely it is that something is going to break on these vehicles, and that really is the bottom line.
I think you are going to be fine with either pulley. Like stopsign said, get her up to around 450, maybe 425 if you wanna be a little more conservative, and enjoy it.