I know this is old but there probably shouldn't be more threads.
I'm not sure why logitech hasn't released a modernized g9x yet. They perfected their sensor/switches/firmware ages ago and pump out tons of weird and awkwardly shaped mouses with it. The g9x is for sure the best shaped mouse for fingertip gripping ever released, and I suppose logitech thinks the g303/g502 are proper replacements for it when they are not at all similar.
I've always hated inadequate sensors or firmware with smoothing/random acceleration/delay and what not but I still use the G9x over the dozens that I've tried. (EC2a, ninox aurora, ZA13, G-pro, G303, G400, FK2, WMO, abyssus, kinzu/kinzuadder)
From my understanding of the G9x sensor, the ADNS-9500, I will give some advice that might make using it more bearable. Laser sensors jitter a lot on bumpy and uneven surfaces, such as low-quality cloth mousepads like the QCK. Firmware is used to negate the jitter and this results in about 5% negative/positive acceleration at random. From my experience using flat surfaces lessens the acceleration quite a bit. I'm not really sure what the flattest kinds of mousepads would be but I'm currently using a frostpad (which is a glass mousepad similar to the icemat).
I'll make a list here of what are likely flat mousepads, starting from the flattest:
icemat/frostpad (the only issue with glass is that it degrades your mouseskates faster, you likely would need a few replacement ones)
any hardpad (I'm not fond of these at all, maybe some people would be)
artisan (the semi-hard/semi-glass ones such as the shiden)
artisan (cloth)
zowie GS-R (this mousepad is high quality & manufactured to be quite flat/durable, unlike the QCK, I am unsure if laser sensors perform any different on cloth pads though)
Another thing is that the G9x tends to jitter significantly if the sensor lens is dirty. You can test if there is any jitter by setting your G9x to the highest dpi and opening paint, switching to the pencil tool and drawing lines/circles. If it's dirty the jitter will be quite noticeable. To fix this just get a q-tip with isopropyl alcohol and rub the sensor. Usually the jitter isn't noticeable at low dpis but maybe it increases acceleration.
Lastly, the bigger shell is better than the precision one. Seriously