Well, good news I thought I'd share, in case anyone ever searches for this info... With the newest BIOS, Secureboot/UEFI *DO* work with Optimus disabled, only running on the Geforce GTX 680m. I was also a little concerned that Windows activation would be screwed up through switching from BIOS to UEFI mode, but thankfully it wasn't. It was already activated by the time I got to the desktop, and it's running on only my Geforce. (Since theoretically Windows 10 can use two GPUs at once, it would be sort of nice if you could run on the Geforce, but leave the Intel GPU active for the handful of upcoming games that might support that, and for things which can use Quicksync, but not Nvidia's equivalent...but mostly who cares, I just want the Geforce as my primary GPU!) I have NOT tried toggling that setting in Windows 10, but at least with the system already set to Geforce-only mode, it remains working just fine even in UEFU mode.