I found that my system was not completely stable at 4.8GHz until enabling Internal PLL Overvoltage. I would leave my PC on overnight and come back to it hard-locked after a long idle period.
As for LLC, I'm not familiar with ASRock's scale, but I'm going to assume that LLC level 1 is equivalent to "Extreme" on Asus boards and should only be used for >5GHz. On Asus boards the highest level equates to overvoltage under load while the second highest "Ultra High" is very close to having no voltage droop at all under load.
For 4.9GHz I would use LLC level 2 for sure, but whether you need Internal PLL Overvoltage on is up to your chip.
---------- Post added 2012-05-09 at 08:09 PM ----------
Cherry Reds are already fairly quiet for mechanical key switches so I never really noticed them. I'm already sensitive to noise, so I just try my best to zone out domed switches and mechanical alike.