It could always be due to hard drive speed, specific things on the hard drive, or the installation of the OS itself. My Cube, at 450MHz, when I had 768 in it, booted ages faster than my 867MHz PowerBook with 640. Moreover, the Cube runs SDRAM, and the PowerBook DDR. Yes, hard drive speed is different, and there's a subtle ram difference, but it ended up with boot times that were miles apart.