Based on what I have seen, if you long load your 7 mm Rem, the difference is about 100-150 fps. The actual effective case capacity differance is about 3-5 grains. The long neck on the Mashburn gives you loading flexability with bullets re. stand-off from the lands (freebore) that the Rem doesn't have.
Max (63-65 K psi.)with a 175 in a Rem is about 2975-3040 fps. in a 24" barrel depending upon powder, etc. I the same barrel length a Mashburn gives about 3075-3130. YMMV.
