Bullfrog,
You have a nice gun. I've shot similar Smiths. They are pleasant with factory loads and can be 'upped' a little over the SAA.
But they are not nearly as strong as a Ruger, and even if they were, you could not stand to shoot Ruger-class loads in them. Trust me, it would hurt. A LOT.
Plus it is really not necessary. Why don't you try a 255 gr. SWC at around 1,000 fps. With cast bullets this is easy. In fact I believe that the current Speer manual gives loads up to this velocity level with their 255 gr. SWC, and the test gun was a Smith 25-? (2? 5? I forget which is a .45 ACP and which is a .45 Colt). As a bonus your sights are more likely to be friendly with this combination rather than something lighter and faster, or heavier.
Personally I shoot a 'practice' load in my Blackhawks which is just this, a 255 gr. SWC at a little over 1,000 fps. Lest you think this is a pop-gun - shoot a milk jug full of water with one. Or better yet put about 5 or 6 jugs in a row and try to recover a bullet. The flat nose kills reliably, and for deer and such you'll have all the penetration you need.
Anyway it sure is fun sometimes to think about the potential BUT sometimes we find that we can have too much of a good thing. I was all hot to build a 5-hole .45 Colt once upon a time, till I actually got around to some 300 grain bullets at the 6-shot level. That cured me of wanting to go higher.
Anyway I encourage to try the above and see if that doesn't meet your needs. Bet you'd be surprised at just how effective the .45 Colt can be, even at original blackpowder ballistics and a smidge higher.
If you really want some comfort in knowing you have the absolute most power out of that round (which would also be safe in your gun), contact Cor-Bon and/or Buffalo Bore Ammo. One or the other of them has a 300 grain load which they say is OK for the Smith DA. One box will probably last for years, and be cheaper than buying all the components to work up your own loads.
Mike