Greg: That 25-5 was produced in 1988. The -5 was introduced in 1978 and was the first standard production Model 25 variation in .45 Colt - prior to that the M25 was .45 ACP except for a couple of special runs in .45 Colt.
As you probably know, factory .45 loads are held to comparatively mild pressures because of the number of older guns out there and the N-frame Smith can handle more - how much more, I'm not the right person to say. I have a 25-5 from 1980 in .45 Colt and I keep my handloads within factory specs figuring that if I need a more invigorating experience at the range I'll shoot one of the .44 Mags or whatever - but that's just me.
That $650 price strikes me as a pretty good deal for the condition you describe - it certainly would be around here, but our draconian gun laws tend to drive prices up for certain guns.