You'll see the most gains via reloading obviously, but most factory ammo uses relatively fast burning powder (mainly for cost I'm sure) which doesn't react as well to longer barrels as a slower burning powder. I've personally seen increases of less than 50 fps between a G27 and a G35 using factory ammo. If you want to use the G22 for deer I see no problem with that, here's an article on just that using factory JHP ammo:

http://www.gunblast.com/JoeRiekers-NewAmmo.htm

As for handloading differences, remember that heavy bullets react less to barrel changes than lighter bullets, but it's possible to to see 150-250 fps in velocity in .40 S&W comparing 4" to 6".