If, like in IPSC, you have to make 'major' power factor (165), the 625 will make it easily with mild loads. For example, a 230gr FMJ at 720 fps makes major... and is mild in a 4" 625, mainly due to the 43 oz mass. The full-lug keeps the nose down, too. A 158gr RN would have to break 1045 fps to make 'major' - hardly a 'mild' .38 load... more of a mild-moderate .357M load. If 'minor' PF of 125 is to be met, you can use a 158gr @ >792 fps, and so on.
I like the 625JM I bought two years ago in February... great shooter - a frugal to shoot 'big bore'. I would also suggest you consider a 620, a 4" half-lugged L-frame 686+ equivalent that replaced the venerable 4" 66, if you can live with the lower PF. It points well and is only 38 oz.
The 625JM I have groups a little tighter than the 625MG's I have in .45 Colt. The 5" 686+ h-l I have groups a bit better, as does my JM PC627 V-Comp. My best groups are with my 6" 66... probably mainly due to the longer sight radius - and that 66's 'pointability'. They are all much better than I will ever experience. On a good day, I can plink away at a 16" steel plate at 100+yd with my 10 and some 158gr LRN/LSWC homebrews, hitting it 2-3 times out of six standing - and freehand. Did I mention it's a 2" 10? I don't have 'good days' quite as frequently as I once did... or those plates have really shrunk!
Stainz