[mickmate]

Bigger is worse with combustion chambers. The smaller chambers give a higher compression ratio and more bang. They also require a higher octane fuel to stop pinking etc. The head rise you refer to are intake port related and valves don't change. The best combination for performance and fit under the bonnet is small chamber, big valves and medium riser. If you do a search there's a lot of head info available.
Cheers Nick