It never ceases to amaze me how fast coreboot boots. Here is my modified version of Libreboot 26.01 Magnanimous Max, on my Dell OptiPlex 3050 Micro (the one I use as my main machine).
I set payload_grubsea="'y" in config/coreboot/dell3050micro_vfsp_16mb/target.cfg and did:
./mk -m coreboot dell3050micro_vfsp_16mb
And there, set debug level to zero, and disabled serial debug output. You can see here that it boots to GRUB in less than a second.
You can really seriously rice it for boot speed.