the grigri is fine to use on ropes above 9mm as long as your belayer knows how to use one, the thinner diameter will run thu the device if your not holding the tail end of the rope as for a non locking atc or something. i was being belayed by this guy on a grigri and he dropped me from 5 bolts up to 1/2 a meter from the ground on a 10 mm rope, when i protested what the f*#k he said, the grigri didnt lock off man.... i asked, were you holding the end of the rope he said, i didnt think you had to!! and this guy was quite an experienced climber! so now i always ask new belayers if they know they need to hold the tail end no matter what the rope diameter ;)

The infinity is fine on the gri gri, I've held many falls on this rope and it's no problem. There are many many out there who belay with the GG on Mammut's 9.2 and sterlings skinny nines and their still alive

Get a Mammut SMART belay device. It works on 8.9 to 10.5 ropes and is a super slick little unit. It pinches the rope and while not a true Autoblocking device like a GriGri it works like one and super easy to hold a fall. Best thing about it is how fast you can pay out rope for a lead belay.

I have this rope and I have used it with my Gri-Gri. It does work but I would suggest not using them. I don't like them in any situation though and an ATC is a much better option in my opinion. I used the Gri-Gri pretty much the same as an ATC locking it off like I normally would. Passive gear which you control is always better.

Probably not. I have a 9.8 that still grabs, but it's a bit sensitive. Hard to control the speed. I think this would be too small. The Faders SUM is an auto-locking device that grabs down to 9.1, I'd invest in that. Or a thicker rope.