Its the compression that determines the use of race fuel not the dome size. Now don't get me wrong the dome size mixed with the rest of your mods will increase compression requiring higher octane, but some of the responses above state that if you run this size dome you have to run race fuel. NOSS had a compression chart available and if you searched on here you would find it and it stated what elevations and what size domes put your compression over the edge for pump gas. Even 20cc domes at 3500-4000 ft would allow pump gas still, but you still need to do a compression test..............
For example: T-5's and a NOSS head with 20cc will cause you to run 50/50, because it puts you at about 150-160 and to keep it from detonating you need to run higher octane fuel, but you don't need to jump straight to 100% race fuel either. If you don't need to run race fuel it is a waste of money until you get higher compression and need it....................