But I am guessing that it doesn't work quite like that?
Actually, when it comes to virtualizing a second operating system, whether it's natively or through emulation, RAM does play a huge role.
Is there much of a difference between 667mhz and 800mhz? A coworker is likely going to be able to get me 4gb of 667mhz ram for free, but if it is noticeably slower than the 800 mhz I would rather buy it.
There difference is, in theory, the factor of speed increase. This is assuming that you always have extra RAM to spare. For example, if you have two computers, each with 16GB of RAM, but one running at 667MHz and the other at 800MHz, application data stored in RAM would in fact be loaded 1.2x as fast.
*But* this is assuming, like I said, that you always have RAM to spare. If those same computers then were spec'ed as follows: Computer 1: 2GB 800MHz, Computer 2: 4GB 667MHz, and you were running Photoshop and operating on a 3GB image file, then the computer with the slower (but more abundant) memory would most likely run faster, since 1GB of the image is actually being cached to and loaded from disk on the "faster" computer, which operates MUCH more slowly than RAM. Hope this helps, and if I'm mistaken in any way, please correct me!