FWIW Bowhunter, A few days ago, I came across a 6" 10MM 1911 type pistol I'd never seen before. It was a Kimber Stainless Target LS/long slide. Price was $999.00. It would appear there is not much difference in price between the 6", and the 5" stainless Target models. I've had a number of 10MM pistols and revolvers, and done a bit of chronographing, but never had a 6" 10MM semi-auto to test. I can say that velocities vary from gun to gun even with same length barrels. I would expect to pick up some velocity with the longer barrel, but I've learned never to predict what the difference will be. With some guns in 9MM for instance, 1" greater barrel length has made a velocity difference, sometimes a little, sometimes as much as ~100 FPS. Were I a hunter, I would prefer the longer barrel, especially when using a higher pressure cartridge like the 10MM....ymmv
BTW, in chronographing .45 ACP we found little, if any, velocity advantage in going to a longer barrel, even out to carbine length. In fact, some .45 ACP ammo produced less velocity in a 16" carbine that in a 5" pistol barrel....