If I got the 21 I would get it with the original style frame which is an extra cost item from CSMC.
My thought is to have an all around gun that I can shoot clays with and hunt with. I shoot clays with my 6 1/4 lb 16 gauge quite a bit.
If I got the Fox it would either be a 12 or a 20. What is interesting about the 21 is I could get a 20 with a set of 16 gauge bbls. I would consider a slim beavertail on the 20 gauge bbls and use that for clays and high volume dove and use the 16 with a splinter for pheasant etc.
It is just a thought. I'm still not sure I'm going to go the new gun route vs. an old english gun. Either way it is looking to be just shy of 20K.
I know these three options are very different but I like all three types of guns for different reasons.
DH
Get a proper fitting. Then, buy an in proof Rocketman tier 1 or 2 British 12 bore SLE and have it altered to your dimensions and requirements. This should cost you 20k or less.
Unless all you are going to shoot is lots of clays then I'd get the 21.