It seems a bit daft to start worrying about getting insanely high DPI on a wireless mouse - wireless isn't going to be pinpoint accurate, so why worry about getting a pinpoint accurate laser?
I like having a couple of side buttons, use them for back and forwards in web browsers and windows explorer, then usually switch to knife and throw grenade in a game. As for adjustable DPI and the like, I think I've only ever used it in games like BF2 where find yourself in a helicopter and want to make the damn thing turn around a bit quicker. Whether it actually makes any difference? I doubt it.
Personally, I think it's a fairly crazy amount to spend on a mouse. I've got a
Gigabyte M6880 (£10) and a Logitech G5, approx £50 I think a few years back. Apart from the grippy surface on the G5 which I really like, I couldn't really pick between them in terms of day to day use and gaming... I honestly don't find there to be any difference, certainly not one that explains the difference in cost.
I'm a big fan of Logitech, because of their brilliant returns department, so I'd probably be looking at an MX518 @ £25 or a G500 @ £35. On the basis of gaming, I'm not convinced by wireless mice, which is why I've not talked about them... I don't know anything worth saying, in effect.
Either way, £70 seems like a lot of money when you can get two G500s for that price.