Hey there,
Well, monitors are a bit more finicky than other hardware to OC. Whilst most panels will do an extra 15mhz, that's typically the max for a lower HZ panel. Sometimes you can get more, sometimes, it's less.
In terms of longevity, well if your monitor is expected to last 5 years (warranty) and with an OC it might last 4.5yrs. It's not been gaged before, so it's really hard to quantify.
Nonetheless, OC the panel. If you get artifacts, go 5mhz lower untill it's stable. Use UFO test to see if it's maintinaing/processing the extra frames.
I've a BenQ 60hz panel running at 75hz flawlessly for the last 4 years.