OK. IMHO....
1. No - as far as I can tell people can use benchmarks to show just about anything. Search hard enough and you'll find that one might be 5% faster than the other in some contrived benchmark, but how much does that matter to you? They'll both be damn fast - applications will be waiting for you, not the other way around - so either is fine.
2. I own a Vaio and I've been very happy with it. Very well made and reliable. Not so convinced by Toshiba, but I know people who are.
3. I've not run XP on a laptop, but on my desktop machine it is completely solid. IE dies from time to time but doesn't cause the OS to die in sympathy. This is progress.
4. I wouldn't buy overseas. It is a saving if nothing goes wrong with the laptop, but otherwise it may cause severe grief. Ask yourself if the risk of being left with a dead laptop is worth a couple of hundred quid saving to you. Also, make sure you try before you buy, even if it is trying at PC World and buying from someone with sane prices.