You should probably also consider that weight will factor into portable comfort in the long run.
The added weight of the PSP 1000 may outweigh the benefits of it being bigger.
But the only way you can find out is testing, so I'd recommend asking people you know about there PSP's if they have one (and maybe to let you borrow it depending on the relationship). Or if that's not possible, you could always go to a second hand shop or gaming store that sells second hand console and ask to check out one of those PSP's (like to be PSP phats) and ask for a play test, that'll tell you if it sits comfortably in your hands. Then say "Okay, thanks, I'll need more time to think about it, but I'll come back later".
Obviously do this at a store that you know you'll never visit again......
But if you discover that you don't mind the weight and like the feel in your hands, your decision will be made for you.