Great review as usual, pzogel. TPU is certainly my go to site for mouse reviews these days.
I've had this mouse for a couple of months now, and I personally ended up using it at 4khz, because I get fps drops with 8khz on some games when moving the mouse fast. Looks like my CPU (6850k @ 4.4) can't handle the 8khz. 4khz is plenty however and I really can't notice any other difference compared to 8khz, except that I don't get fps drops on any games with it.
That being said, this is by far the best tracking I've experienced with any mouse during my 15 years+ of afps gaming, and I'm surprised how much of a difference the higher polling rate actually makes. It's smoother, but most importantly it feels noticeably less delayed movement wise.