Summary: Let's just get to the temps, that's what we are here for, right? :) *** CPU: quad-core Intel Core 2 Extreme QX6700, at stock 2.66Ghz, rated 130W. CPU fan: [high] 2,500RPM. Case, fully closed: Antec 900 (front: [high] 2 x 120mm, side: [medium] 1 x 120mm, back: [medium] 1 x 120mm, top: [low] 1 x 200mm). Compound: Arctic Silver 5 (paste) or Zalman ZM-STG1 (lacquer) with identical results. Ambient: a typical NYC summer day, ~27C, no A/C. Worst-case results reported by CoreTemp: completely idle (CPU drops down to 1.6Ghz): core #0: 37C, core #1: 34C, core #2: 36C, core #3: 33C. The ~5C difference across the first and the last core has been there before with other coolers, I need to lap the heck out of my CPU sometime. Stress test with OCCT, continuously murdering all cores at ~97% utilization for 30 to 60 minutes, worst-case: core #0: 68C, core #1: 63C, core #2: 67C, core #3: 63C. Thus, ChillTec Ultra is indeed capable of handling a QX6700 at any load under less than ideal ambient conditions. *** Moving on to overclocking... Worst-case results for 2.93Ghz (10% overclock), stress tested with OCCT: core #0: 70C, core #1: 65C, core #2: 68C, core #3: 65C. The system remained perfectly stable, but as QX6700's maximum thermal design specification is ~65C, this test should be considered a failure (who cares that a QX6700 actually fails all the way up at 95C, that's not a sensible way to do it). Cooling ambient well below 20C with A/C, opening up the case, stress tested with OCCT, yielded a bit better worst-case results: core #0: 63C, core #1: 58C, core #2: 61C, core #3: 59C. A success, but surprisingly small difference for a ~10C drop in ambient, which suggests to me that the problem here is probably hitting the limit of Ultra's overall heat exchange capabilities, rather than PC case airflow or HSF seating. *** To summarize: ChillTec Ultra will indeed run your QX6700 safely at stock speeds without having to worry about providing perfect ambient conditions. However, if you want any quad-core overclocking, be ready to either run your A/C full time and open-up your case, or find another cooling solution. What I would like to see in the future is someone taking a Thermalright Ultra120 Extreme and slapping a ~75W TEC on it :).