I think you want to run at least 10% nitro, but I'm no expert either. I ran only 10% for a long time and was amazed at the increase in power when I switched to 15% in my TT Pro 46. On the other hand, I have an OS 46 that will not run on 15% on a hot day.

As to the Voltwatch, I just installed my first one last week and it seems to be giving fairly accurate indication on on-board voltage - I've been checking it against my voltmeter. I like having a visible light to at least tell me that I forgot to turn the darn switch off. I've also read here that the voltwatch can provide an indication of an electrical problem. If the lights are flashing all over the place when operating the servos, something is amiss. IMHO, Voltwatch is cool, but don't rely solely on it. You still need a voltmeter.