My wife has a m2 26" and I have a sx3 26".
Both are great guns and will blow your minds with the patterns they can produce.
I have ic chokes for both and they are very comparable. The best pattern I've ever gotten with the 1 5/8 tss loaf was with the m2 and 555 ic, 378 in the ten. This was the best, normally not quit that good.
To me, if I was buying again I would handle both and pick the one that handled best for me.
The recoil is a lot less with the sx3 gas and weight advantage but on the other hand the m2 is a feather to carry around.
I would not be concerned about the pattern as I think both will pattern better than you expect if you never shot tss.