John Linebaugh, the big-bore guru, considers 32,000 psi to be ABSOLUTE MAXIMUM for this gun and prefers to hold his personal loads to 5% under that for approximately 25,000 psi. He feels that the stock cylinder isn't strong enough for safe use beyong that pressure.
Since Ace Custom rates the hottest .45 Super loads at 28,000 cup (don’t know the psi conversion), I suppose that you’re in the big "if" zone with the 625. In the course of time, all the little parts wear a tiny bit and soon adds up to a lot of play in the overall fit and lock-up of the gun. S&W has done a lot to improve the N-frames over the years, but I don’t shoot .45 Super in my 625 Mountain Gun. I don’t want to batter it and .45+p is plenty stout for me in this gun. If that isn't enough power, I go to the .44 Magnum.
I suppose an occasional .45 Super foray -- say for hunting -- would be ok, but a steady diet -- not for my beauty. I have a modified Glock 21 and stock HK USP for .45 Super use.