I would hold off at about 8lbs on a stock motor if you want it reliable in the long run. You will need head studs just to keep the head down, but other than that, the stock motor can handle the 8lbs real well.
Part of what Kai was getting at, is that 8lbs on a T3 is moving a lot more volume of air than a t25 at the same boost, and a smaller turbo like a td04 would flow even less at 8lbs. Same pressure, less volume.
www.homemadeturbo.com and www.turbod16.com at going to be some good resources for you. And as much as I hate to say it, but there are some Saturn guys out there on 1 message board that I've seen that KNOW their shit. They are basically the Saturn pioneers, like the honda guys were 5-10 years ago that were boosting. Those guys are very open with info, and there are a bunch of turbo maps posted on the site. I'm blanking on WHICH site it is though... :doh: