Overclocking
The stock voltage on our Q9300 was 1.2V. On the very first attempt, I raised the base FSB clock from 333MHz to 425MHz, and the Q9300 was stable—at 3187MHz, stock voltage. Some additional tinkering didn't yield much more. I managed to reach 3.26GHz on a 435MHz FSB by raising the Q9300's voltage to 1.225V. Beyond that, additional voltage didn't seem to help. After tweaking the memory a bit to match (1392MHz with 9-9-9-24 timings), I ran some benchmarks.

The Q9300 at 3.26GHz

Next up was the E7200. My first attempt, of course, was to reach a 1333MHz bus with the default 9.5X multiplier. The E7200 was more than happy to comply, booting into Windows and passing our Prime95 stability test effortlessly at 3.16GHz. This was, incidentally, at its stock voltage of 1.175V. Rather than stop there, I kept pushing, finally ending up at 3.372GHz with a 355MHz base FSB clock—at only 1.2V. I set the memory clock to 1182MHz with 8-9-9-24 timings for testing.

Both processors, then, reached beyond 3.2GHz without much drama. Going much past that proved difficult. We've seen a pretty good range of Intel P35-based motherboards, including the DDR2 version of our Gigabyte P35T-DQ6, reach 490MHz and beyond, so we weren't likely being limited by the motherboard. I was using a mid-sized air cooler with aggressive fan speeds, nothing fancy, but I doubt additional CPU cooling (short of an exotic chiller) would have helped. Neither CPU was reporting temperatures much beyond 50°C under load, and the overclocking failures typically came during POST or Windows boot, not under stress. Also, my Q9300 overclocking results freakishly mirror exactly what Geoff saw out of the Xeon X3320, a differently badged version of the same processor. Your mileage may vary, of course.

Here's a quick look at the performance you can expect if you overclock these CPUs to these speeds. I've thrown in some results for other overclocked processors, as well.

Note that, at least in these tests, our Q9300 overclocked to 3.26GHz beats out a Phenom X4 9850 Black Edition overclocked to 3GHz.