I'm trying to find some Shearer pipes for my bike. I'm definitely getting a 68mm cub. Depending on how my play money goes, is depending on whether I stick with the 4mil, or get a 10mil. I intend on building the 10mil, but cash is tight. Now, if I buy big bore pipes, and I end up staying with the 4mil, would they hurt the performance? I know, the more your engine can breathe, the easier it is to make horsepower. But I'm thinking the big bores might not be enough back pressure for the 4mil. Any thoughts would be appreciated.