I've thought about this before, too.
A 300 grain bullet at between 900 and 1,000 fps would be just fine, with maybe a 260 JHP at 1050 fps.
John
edit- hey, waitaminute! You said self-defense loads. You mean against people? Are they wearing body armor, or do they just grow them really, REALLY "big 'n tall" where you are? A self defense load from a sidearm should be controllable enough for a quick second (3rd, 4th, 5th, etc, as necessary) shot. Sidearms are, by their nature, underpowered, so don't expect one round to do the job. (The only exceptions to this rule are so heavy and cumbersome that one would do better to use a should arm, at any rate.) Aside from that, the extra power you can inject from a really heavy load from something like a .44 Magnum can only be used with a relatively fragile (usually lightweight) bullet, to rapidly expand and probably fragment. An example of this could be a well-designed .44 185-grain JHP approaching rifle velocities. If you just drive a tough bullet a few hundred FPS faster, all you're doing, is giving the bullet more penetration to use on the next thing it hits...may it not be an innocent. If you're planning a genuine self defense load-and rolling your own- at a minimum with something like this, you should do penetration testing in water. If you're using a heavy lead bullet, I think you'll find that "more than adequate" penetration out to 50 meters is achieved with much less velocity than your current goal. (Again, if you're planning on engaging kevlar-garbed goblins or men with chests 25" deep, ignore all but my first two sentences.)