Regarding velocity of the two - I know this is goint to sound crazy, but.....

Here are actual 5-shot velocities I got with 250 and 300 grain Gold Dots over 100 grains T-7 FFG and Harvester Crush Rib sabots.

250 grain bullet: 1901, 1653, 1626, 1794, 1834 = 1761 fps average.

300 grain bullet: 1731, 1730, 1727, 1766, 1735 = 1737fps average.

Got a 3" 50 yard group with the 250s, and a 1 5/8" group with the 300s.

Notice the velocity spread with the 250s.

I don't explain 'em - I just report 'em.