I own a 6.5" 629-5, purchased just this spring. To date, I have about 550-600 rounds through it, a 50/50 mixture of 1200 fps 240s and 1000 fps 180s. Here's some things I think:
(1) Recoil with full-power 240s is not excessive. However, a proper technique is necessary--absolutely no locked elbows! You'll feel it the next day. You'll also have to be actively on-guard against developing a flinch. 180/200-gr loadings are downright mild in a frame this heavy.
(2) The 629 is more than capable of true .44 Magnum loadings: 240-255s at 1200 fps or so, which are accurate and quite entertaining (water-filled milk jugs leap into the air). What it's not designed for are the loadings that massively outstrip the original design specs. If you want to hurl 300-grain rocks downrange, get a Ruger, Freedom Arms, Dan Wesson, or a .500 S&W Magnum. It's not that there's anything wrong with the N-frame--it's quite good at what it does.