I made the mistake of trying on the 40mm pilots watch at a jewellers. I need to start saving immediately. I was going for the Omega first watch on the moon but when I put this on it fitted like a glove!
You really can't go wrong with either of your stated grails; I really like the look of the Zenith, and if it fits, wear it! I can't comment on the 681 movement (there are other experts on the forum who can give you loads of info), but it is a very nice design, and looks good on the wrist.
I know I have strong bias, but for me Zenith should be chronograph AND El Primero . The other versions are just complimentary.