Paulosantos, considerate and well informed moderator on 68forums.com provided me with the following information about velocities in different barrel lengths with similar specifications.
Here are the velocity differences between a 14", 16", and a 20" Ko-TOnics Barrel:
14" Barrel: Ko-Tonics 16" chrome lined barrel with the 1:11" twist.
16" Barrel: Ko-Tonics 16" chrome lined barrel with the 1:11" twist.
20" Barrel: Ko-Tonics 20" chrome lined barrel with the 1:11" twist.
Sierra 90 Gr. HP with 28.5 Gr of H4198:
16" Barrel: 2902 fps Average.
14" Barrel: 2796 fps Average.
Difference: -105 fps.
Sierra 90 Gr. HP with 31 Gr of H322:
20" Barrel: 2927 fps Average.
16" Barrel: 2821 fps Average.
Difference: -106 fps.
14" Barrel: 2607 fps Average.
Difference: -214 fps.
Speer 90 Gr. TNT with 31.5 Gr of H322:
20" Barrel: 2933 fps Average.
16" Barrel: 2804 fps Average.
Difference: -129 fps.
Speer 90 Gr. TNT with 30 Gr of H322:
20" Barrel: 2817 fps Average.
16" Barrel: 2671 fps Average.
Difference: -146 fps.
Speer 90 Gr. TNT with 28.6 Gr of H4198:
20" Barrel: 2984 fps Average.
16" Barrel: 2854 fps Average.
Difference: -130 fps.
14" Barrel: 2821 fps Average.
Difference: -33 fps.
Speer 90 Gr. TNT with 32 Gr of X-Terminator:
20" Barrel: 2829 fps Average.
14" Barrel: 2676 fps Average.
Difference: -153 fps.
Speer 90 Gr. TNT with 32.5 Gr of X-Terminator:
20" Barrel: 2899 fps Average.
14" Barrel: 2747 fps Average.
Difference: -152 fps.
Hornady 110 Gr. BTHP w/Cannelures with 29 Gr of H322:
20" Barrel: 2692 fps Average.
14" Barrel: 2462 fps Average.
Difference: -230 fps.
Hornady 110 Gr. V-Max with 29 Gr of H322:
20" Barrel: 2688 fps Average.
16" Barrel: 2607 fps Average.
Difference: -81 fps.
14" Barrel: 2436 fps Average.
Difference: -171 fps.
Hornady 110 Gr. V-Max with 25.3 Gr of H4198:
16" Barrel: 2523 fps Average.
14" Barrel: 2456 fps Average.
Difference: -67 fps.
Hornady 110 Gr. V-Max with 29.5 Gr of H335:
16" Barrel: 2585 fps Average.
14" Barrel: 2403 fps Average.
Difference: -182 fps.
Sierra 110 Gr. Pro-Hunters with 29 Gr of H322:
20" Barrel: 2670 fps Average.
16" Barrel: 2534 fps Average.
Difference: -136 fps.
14" Barrel: 2400 fps Average.
Difference: -134 fps.
Sierra 110 Gr. Pro-Hunters with 29.5 Gr of H335:
16" Barrel: 2494 fps Average.
14" Barrel: 2423 fps Average.
Difference: -71 fps.
SSA 115 Gr. Enhanced SMK with 28.2 Gr of H322:
20" Barrel: 2558 fps Average.
16" Barrel: 2461 fps Average.
Difference: -97 fps.
SSA 115 Gr. Enhanced SMK with 24 Gr of H4198:
20" Barrel: 2459 fps Average.
16" Barrel: 2343 fps Average.
Difference: -116 fps.
I hope this helps. Have a good one!