Thank you, persmule. Given your positive experience with the newest nightly, I went ahead and flashed 22May2016 on my t400 (I didn't compile from source--just grabbed the rom from downloads page).
I can confirm that the graphics problem is gone. I am also happy to confirm that the date and time are correct after a reboot with linux 4.5--no workarounds required. Still can't resume from suspend, but that's a minor issue as I almost never use suspend. I'm not sure what you meant by "graphic output for grub", but I can see the grub menu and background image just fine. I'm on Debian GNU/Linux stable, with a small handful of backported packages (including linux kernel 4.5.3-2). Jessie's default kernel (3.16) seems to ignore the "intremap=off" boot parameter, due to which I was getting an error during boot having to do with interrupt mapping/dmar. With this latest libreboot, I can now run kernel 4.5 which complies with "intremap=off" and therefore I get no errors whatsoever during boot. Very nice. Thanks for the helpful information.
