MX 3000.
I found it lagged in games, when using the keyboard and mouse at the same time in say BF2 i got lag.
I could also notice slowdown when touch typing in a word doc for example.
I had been using cordless keyboards for a while and just accepted it. But its not till i recently purchased a wired g15 and a mx518 mouse that i have really seen how bad it was.
Im sticking with wired for the time being.
MX3000 setup is a nice bit of kit though, good tactile feedback from the keys and the mouse is good, feels quite comfortable in the hand. Just depends would my above points affect you in anyways?
edited the mx5000 i had was bluetooth lol, also had similar issues with that

best cordless keyboard and mouse which i havent had issues with would be the di novo ver2
Another note for you to consider, if you have small hands the mouse might feel a bit big, but it is comfortable