Old fx impact power plenum vs newer 72cc pp.

Have anyone compare the old pp on the mk2 vs the new pp on m3? I heard the old pp is like 54cc vs 72cc. How much more speed/power would you get from just upgrading from old pp to new pp and is it worth additional $200?

Example if my gun is shooting 970fps with 36gr nsa slug, without changing any setting and just upgrading to 72cc pp, how much more speed/power should I expect?