In that case, download everything!
I like to spend the time and effort (too much and too much) downloading &*#% everything and unzipping/unraring/unwhatevering it onto a flash drive (or two). That way I have it all on-hand.
Then I typically have a few windows installs, XP, Vista and 7, on a hard drive, with the flash drive copied in its entirety onto the desktop.
Then I typically have a second hard drive done exactly the same way, but with the other manufacturer's GPU drivers. That way I can bench both AMD and Nvidia without having the drivers start fighting.
I tend towards overkill.
To start off with, make yourself a benching HDD with an install of something and install the benches and run with it.
If you're benching competitively doing it on your 24/7 OS is a bad idea. For one because it's slower, and for two because your benching OS will die eventually.