Our $2,500 PC used the same Intel Core i7 920 processor that the $1,250 PC did, but with a much larger CPU cooler. Extensive testing allowed us to find a maximum CPU clock speed of 4.42 GHz at 1.45 V core, but that was in a cold room.
When the room temperature warmed up, we found that even our monster-sized Vigor Monsoon III LT wasn’t adequate for cooling Intel’s latest CPU architecture at such a high voltage. Cooling the lab was not an option since we wanted our settings to reflect real-world results that our readers could—with some luck—copy. Hours of additional full-load testing revealed that no more than 1.3875 V could be used at a room temperature of 75 degrees Fahrenheit (23.9 degrees Celsius). At that voltage, we were still able to reach 4.00 GHz at 200 MHz reference clock.
Raised CPU VTT, QPI, and IOH voltages kept our CPU stable at the higher reference clock, while a DIMM voltage of 1.65 V allowed our memory to run at tested speeds up to a 1,720 MHz data rate. After settling for a 200 MHz reference clock, our Super Talent DDR3-1333 responded favorably to CAS 9-8-8-16 timings at DDR3-1600. One problem we encountered with the EVGA X58 3X SLI motherboard was that tRFC had to be manually increased to allow any significant overclocking—this type of adjustment is normally done automatically by the BIOS of competing motherboard brands.
We tried overclocking our graphics cards, but one was already at its maximum stable speed. The likelihood of receiving a non-overclockable card increases with the number of cards used.