RB 5 port is a strong mill and should keep up fine with the X12. I wish I had a long straight. I have a 5 port V12 Rody sitting in my box just waiting for enough room to stretch it's legs. It's certainly more engine than I have room for locally. I run a 3 port V12 most of the time, and it seems to run as well as the Mugen X12 also. It has a little less top end than say a JP mod or some other modded 3 ports, but it's also considerably cheaper. If I were to buy the V12 3 port Rody I'm sure it would perform more like the other mods available.