With my SB750 ASUS, I decided to stay with 3.2Ghz (1.375v) even though higher clocks are possible. For example, my external (non-mobo) temp sensor on mosfets was spiking to 55C on high overclocks and I was getting BSODs that were odd. I concluded that even though my cpu temp under water was 44-46C under very heavy load, that other chips on my mobo were too hot.
Regarding cpu tweak, I found about a 9-10c difference on idle and 4-5C on heavy load. I leave it off and see no difference or slight increase on benchmarks. I don't like heat for little gain.
Bummer about your retailer. I think you posted earlier that the guy was giving you odd vibes about ship dates?
Bookmarks