Really good comments guys, thanks!

Phil - at the time I wrote this post originally my mast did not rotate very well at all - my (who knows how old) teflon bearing was a mere sliver. I replaced that with a circle cut from the plastic lid from a peanut butter jar (a temporary solution) and it rotates much better now; again I didn't notice the speed difference as much on Sunday so if mast rotation can affect it that much then it might be that.

Thanks again!