It's hard to say "how much boost" it can handle - since boost can be a factor of many things, but as far as power goes, 250 HP is roughly what has been said the rods can handle - and that was also on a nitrous hit.
I've been pushing around 250 HP for 13.5 years now (with a supercharger), and the car seems to still be happy...but that doesn't mean I don't have a weirdo of an engine and that all of them will handle that as happily as mine has.