I did some local optimizations and have some more info.
I disabled keyboard init in coreboot-v2 - saves 400ms.
I disabled ATA reset in SeaBIOS on first boot.
I exit out of a CBFS search in SeaBIOS if the file signature is zero (CBFS is zero padding instead of ff padding).
This brings the boot time on reset to 1.7 seconds (reset press to grub launch - doesn't include 2.5 seconds at boot menu). Boot from powerup takes a bit longer - 8.9s (7 seconds is for drive spinup).
Another optimization I could make would be to reduce the 90ms it takes to copy the vga rom from flash. Using 4 byte reads instead of 1 byte reads will likely help. However, enabling an mtrr for the flash would likely lead to the best results.
I'm not sure if I'll commit these changes - it is something to think about though.
Logs attached. This setup, for what ever reason, puts a null byte to serial on target machine power up and reset press (but not reset release, so resets are off a little bit). I'm using this to time the rest of the results.
-Kevin