Efekkt: 90C is too hot. You need to find a way to run that chip cooler if you want to push it to 4.2 GHz or beyond.

RealTemp reporting a multi of 20.5 is usually a very good sign that Turbo mode is becoming disabled at full load. This can happen depending on your bios if you are drawing too many amps.

I wrote a separate utility called i7 Turbo that does a good job reading the multiplier. It uses high performance timers within Core CPUs and is the Intel recommended way to accurately read the multiplier. You can download and read about it here:

http://www.xtremesystems.org/forums/...&postcount=918

I'd be interested to see what it says when you are running Prime Small FFTs at your present overclock settings. Here's the latest version of RealTemp 3.20 as well:

http://www.fileden.com/files/2008/3/...alTempBeta.zip