I'd imagine that would still boost the speed a little, as the PC doesn't need to hand off control to a whole new environment. However, it doesn't take all that long to make the transfer, for one (although changing the VGA mode does take a little time), and the major boost in speed that Coreboot gives you is that it's especially tailored for speedy boot. UEFI is in essence an operating system in and of itself, so it takes a while to load it. Coreboot is just an extremely small program that does one thing and one thing alone, initialises hardware and hands over control as fast as possible. So using Coreboot would still be noticeably faster compared to UEFI direct boot to Linux.
Originally Posted by russofris