Unless you swap out the pistons, your compression ratio will be below 8... using a thinner head gasket is not even an option and hence if you have the stock EJ22T and you mate it to the RS SOHC head, you get something like 7.7:1 compression which would make the low end gutless. I believe the only DOHC head worth using is the JDM STi heads, otherwise it's not worth the trouble - even JDM heads are just too pricey to come by itself.