Logitech MX518 versus G5

I am going shopping for a new gaming mouse, but I'm wondering if I must spend the extra cash (it's a third of the price to buy the MX518). I'm presently stuck with a standard optical mouse, so I wouldn't know the difference in feeling between the Logitech MX518 and the G5.

Basically, the MX518 does 1600dpi and the G5 does 2000dpi. Do these extra dots per inch make that much of a difference? They both say you can drop down to 800 and 400 dpi in-game, so does going from 800->1600 or 800->2000 make it better?

That MX Revolution looks really pretty! The problem I would have with it is the fact that it's cordless! I hate it when the batteries die mid-game. Also the mice are heavier because of the batteries within. The last cordless mouse I had tended to go into power saving mode after 2 minutes and needed to be shaken a few times to wake up. Maybe I'm just biased because of one cordless mouse?