So if the board utilizing this UEFI fast boost tech yet needs time to figure out the RAM config... Wouldn't that mean the board would be contradictory to itself. Have you looked into the specifications of this board as to how it configures the RAM while having the fastboot option enabled? This may be the case with other mobos but I would be inclined to say not necessarily with this board since it's a different tech than other boards you are getting your spec information from.
Don't get my wrong, I'm sure some start up processes and what not will be lacking but it couldn't be that much. I'd say if no one comes up with the correct answer, call the manufacturers. They'll give you the right answer 9 out of 10 times. lol