Yes, you want to max out the power limit. This will make sure that the cards doesn't throttle as much if it reaches the power limits. This has by the way nothing to do with voltage (don't change voltage because that can actually reduce the lifespan of the card). But maxing out the power limit slider is ok.
+500Mhz on the ram seems good and reasonable. But you are already close to the limit. As long as you don't see any artifacts and crazy colors you should be fine. In regards to the +220Mhz it seems to be on the higher end. It really depends on the card. Important to check.....see how constant the clock rate is during gaming, if it changes too much down and up you might want to set the clock rate overclock a little lower. You might...