[n-ster]

RAM temps are not important (as in are very cool) until you reach the 1.8V +. lower timings are better, therefore, 6-7-6-18 1T is better than 7-7-7-20. Yes switch XMP off and put 1T

May I know the rest of your system and your current CPU cooler? Please note that temps up to 80C are OK/good for the i7 920, so don't be afraid to overclock more if you want. 85ish are OK temps, and over that is hot. 90C is acceptable, but hot. 75ish is good/cool, below 70C is cool/cold

EDIT: going from 2T --> 1T is about the same as going from 7-7-7-20 to 6-6-6-18 performance-wise. 6-7-6-18 1T is very possible with your sticks and you should definitively try that.

However, depending on the time you have and how important system performance is to you, higher clocks will be more beneficial then tighter timings. If you want to further improve your computer, going to higher clocks like 1866 7-8-7-24 1T may be better. If you can get 1866 7-7-7-20 1T even better. Please put 1.64V or 1.65V for this however. Do not worry, about these voltages as they are completely safe




EDIT2: may I know what you use your comp for? This way I can help you better and suggest better fitting overclocks.