Ease of fitment 10 valver. Max power attack- 20 valver.
Chap in the states (jared? Javed? ) was running 500bhp on a 10 valver for some time.... not to be ruled out in the persuit of grunt id say.
10 valvers got less moving parts, less complex but less overall scope for power.
Swings and roundabouts and really depends as others have said, re, what youre looking to accomlplish.
