Most of the 920 D0s I've played with require at least 1.30v to run 200x20 100% stable. If you're already looking at 70C @1.18v you'll probably want better cooling before you go much higher.
Should you call it good? Probably, unless you feel the speed is lacking. 4ghz is a "magic" number that everyone likes to see, but it takes good cooling, more power, and makes more heat.