I have a Logitech Cordless Keyboard, one of the older ones, and a Cordless Microsoft Inteli Mouse Explorer Optical Mouse. As far as the keyboard goes I can't remember the last time I changed the batteries in mine and it still works just as good as the day I bought it. I don't see any lag or anything with games. As far as the range, I'm thinking 6ft is the norm for that one but that is pleanty for me. I never goes to far from my desk, but I finally get rid of one less cord behind my desk.
As far as the mouse goes, it uses batteries faster than anything I've ever seen. LOL I'm changing the batteries every 2 to 3 weeks it seems. Make sure if you do go cordless mouse you get 2 sets of rechargable batteries and a recharger, one set to use and one set to always keep charged when you need to change. As far as using it for games, it does take a little getting use to. Whether that is because it's opitical or cordless or both I don't know. I for one play alot of Battlefield 1942 and I've gotten pretty good sniping with it. Like I said, once you use it for a while and play with the speed some you will like it. One note about how I have mine set up. I'm using medium acceleration and I have the speed set a little more than half way, this is in the software setup for the mouse. As far as my games go I have the speed set about half, sometimes a little less.