You're using a MacPro, right?
By all means, use the unifying receiver instead of bt (if you're using bt).
The Logitech mice will work better using the "Unifying receiver" with its own radio "band" -- instead of bluetooth.
Also, instead of the Logitech software, I suggest you try either of these:
- USB overdrive
- Steermouse
Actually, try them both (but not at the same time).
Then pick which you like better.