Perhaps the action is capable of more rounds per minute, but neither was issued as a full-auto, so that's not really an issue, is it? I'm real sure that I could shoot more rounds with the M-14 in one minute, because of the 20 round magazine vs. the 8 round clip. I think this advantage outweighs any other mechanical cycling advantage the Garand may have.
A sniper convinced me that the time it took to lock the magazine slowed the M14. The M14 did come out full auto but it was almost uncontrollable. Open sighs in a fast match type shootout the M1 Garand wins.