Well, a single hispano shell should have quite more power than MG 151 shell, IMO. The kinetic energy is some 50% more in favor of hispano, by the numbers Mandoble gave.
It is amazing how it affects the arena though. Right now vast majority of Spits and cannon Hogs in arena follow the Santa way: HO HO HO.
I honestly can't remember that I have seen any of those planes actually avoid HO.
But that will change with the introduction of pair of MK 103s

However, I believe the best qualities of MG 151 (compact, reliable, can be synchronized, better ammo fuzing mechanism) are not that important in this sim as they were in real life. Also, wasn't MG 151 ammunition (M geschoss etc.) more advanced than hispano ammunition ?
[This message has been edited by Hristo (edited 03-13-2000).]