Shimano SPD cleat float

Sprool

Is there any difference in the degree of float between the shimano cleats - normal SH-51 and the SH56 multi-release types?

forward_loop

iirc correctly - no, I always went with multi release though

diy

No - I have never found any downside (other than the extra cost) of using multi release. There are some downsides on MTB, but for road I actually find that I can run the binding tighter due to the trust that I can pull them out more naturally.