MaximumPC magazine has loved the MX700 for gaming since it came out.
I've never read of a gamer who didn't think the MX700 was the top of the wireless food change with no lag gaming difference from the best corded mice.
The MX900 has the same MX engine as the MX700.
I'm looking for a great deal on an MX700. My 98SE partition wont work with the MX900.
www.tomshardware.com has a good comparative article on the MX engine and M$'s wireless engine from October 20, 2003.
In their opinion, there are two companies and three engines to consider.
The Optical Mice Rat Race Reviewed
http://www.tomshardware.com/consumer/20031020/index.html
They conclude that, "If you're really into precision and frag, what you need is a Logitech MX sensor."
They note that the M$ wireless rodents are designed more for desktop applications rather than gaming.
Here's an article on the MX line from January 2003 ...
http://www6.tomshardware.com/consumer/20030110/mx_mice-08.html
To conclude, here is a mouse that performs just as well as the previous model and, for the first time, the lack of cord does not make it suffer from lag. If its weight, ergonomics and, especially, exorbitant price are not a problem for you, then we can do nothing other than recommend the MX 700. More generally, Logitech have come close to mouse perfection with the MX range. And don't think that all my ramblings about precision and speed are worthless: you should never forget that the mouse is the main interface between person and machine. Our pleasure in using a computer is partly due to the ease of using the mouse.
Here's their latest article on a corded rodent from March 17, 2004.
Fast and Furios: Razer Viper Mouse Goes Optical
http://www.tomshardware.com/game/20040317/razer_viper-05.html
Conclusion:
Razer has a potential success on its hands. This is the ultimate mouse for gamers and graphic designers. It's light, ergonomic, accurate, sensitive and reactive - what more could you ask for? The supplier now only has to design a wireless version that is just as fast as its latest mouse.