Well, if you want an intermediary in velocity (1250ft/s vs. 2750ft/s), then you should go with the .22 wmr, which is about 2,000ft/s, pretty perfectly in the middle.
If you want an intermediary in energy (150ft-lbs vs. 2900ft-lbs), then you should go with either the .223 (1250), .204 (1300), 5.45x39 (1400), 6.8mm SPC (1600), 7.62x39 (1600), .22-250 (1750), or .220 (1750).
If you want an intermediary in recoil (essentially 0 vs. 20), then you have the .243 (9), 6mm (10), .257 Rob (10), .25-06 (11), 6.5 Swede (11), or 6.8 SPC (8).