It is posible to hit 3.6GHz on air with the D805. However, you'll have temperatures in the 50C range, which is on the high side. Not to mention that it's bandwidth-starved by the 533MHz FSB. You'll need to overclock to 4GHz to have the 800MHz FSB that's standard on all other Pentium D's.
The D915 runs cooler, overclocks better, and owns the D805 at stock speed. If you can get 266MHz FSB, you'll have a 3.73GHz CPU, with the same clock speed and FSB as an EE965.