If you book AF through Delta, the fees are very very low. Same with booking Air Berlin using Avios. So you can transfer to Avios (esp. if there is still a bonus) and then book AB out of Vegas if there is availability. Direct flight, low fees. Air Berlin and Aer Lingus are the BA exceptions.

Delta holds your flights, so you can transfer your MR but it's almost instant anyway. My experience with Avios is the same - instant - but they don't hold tickets from my experience.