I have never noticed any of my drop aways effecting the speed of the bow. If anything it might be 1 fps or something, might even make it a bit faster by the same amount. Technically it shouldn't change anything. The only rests I know of that would effect speed would be the whisker type rests, and even that can be minimized with some trimming.

I doubt a chrono would be accurate enough to measure the gain or loss from from switching to a drop away rest. Unless one of your set ups was wrong.

Paul