Razer Naga... It's clicking without clicking!
Honestly though, PvE-wise if you're good at clicking then you'll not really notice a hell of a lot of difference once you've transitioned to keybinds. Of course it IS an improvement but we're talking like 95% vs 100% (with 3% being improved spatial awareness and the 2% being mouseturning) - anyone who says otherwise is just being an elitist for the sake of it.
I clicked since beta, finally moving to the Naga a couple of years ago simply because I felt I "should" and it's not a massive difference at all. 6+ years of clicking quickly builds you peripheral vision up to near-superhuman levels ;-)