[JoshTriplett]

8 seconds for the BIOS sounds ridiculous; that should take less than a second. Check that you've booted and shut down successfully on the prior boot; with those, the boot should take much less time. (On an improper shutdown, the BIOS may do some extra work that takes longer.) Also check that you don't have some option enabled to make it wait around a while for a keyboard key.

For the Linux portion of your boot, try running "systemd-analyze plot > /tmp/boot.svg" and looking at that. (Also note that "kernel" includes any time spent waiting in the initramfs for you to type your disk encryption passphrase.)

[dom0]

Unsurprisingly UEFI didn't change much about vendor firmware shittiness. There's also still firmware around which just takes 5-10 seconds of black screen before doing shit.