I would stick with SPDs, easier to clip in, easier to walk, cleats last longer.
Only reason I have SPD-SLs on my road bike is because I didn't know any better and that's what everyone else was using. There's a lil more float with the SPDs, and the cleat is bigger on SPD-SLs, so I guess there's potentially a watt or two lost there, but for the benefits of SPD, it's not worth it, imo.
I prob won't switch my road bike, because I already have the pedals and shoes, but just like disc brakes, going forward I'll be sticking with SPDs on future bikes.