Most manufacturers of OC-able (up to) 120Hz monitors will state they don't recommend multi-card setups and will encourage a 96Hz refresh rate rather than 120Hz. I wonder why?
Probably because the panels themselves are not designed or rated for the drive voltage/current necessary to switch pixels that quickly, which usually translates into accelerated aging and increased failure rates.
I've had several 2b cats for almost 2 years and brightness is the same and other specs are dead on what it was (using my colorimeter). Haven't seen anything yet that says I am ahead of the 4-5 yr lifespan on the IPS panel. Just my panels of course.
Just curious... Are you running an SLI or crossfire setup with these monitors?
SLI for the entire time (with different cards from 500s to now 780s). No issues.
The sad fact is the manufacturer does not guarantee this OC performance and do not see it as a product defect if you cannot achieve the 120Hz on these monitors so there is a bit of luck involved with this. You are one of the lucky ones.
Honestly if you cannot get at least 110Hz then there is an issue - which by their chekcs every panel meets. 120Hz requires manual timings in many cases due to your rig. Very easy. Even at 110hz I would take that over anything else.