what dome size for a cool head on my 250r?

[j450rking]

i need to know what size dome i should run so i can still use 93 pump gas. i don't want to be on the limit so i want to run the dome one size down from the limit. i need to know asap.

also it's the older style that uses a head gasket so i will be running a stock thickness cometic head gasket

THANKS!!!