Time is probably your most important resource here. Shaving a few nanoseconds off a query because you compiled your kernel with one different option won't do you much good, whereas an easy to administer OS with readily available binaries will save you a lot of time and headache.

I'd say 64-bit Debian. I have already mentioned my qualms with Ubuntu elsewhere on HN (I don't like upgrading every 6 months, and I don't want to be stuck with old software in case I decide to skip an upgrade).