Depends on your rpm range.....
PERFORMER® MANIFOLDS (Idle to 5500 rpm)
PERFORMER RPM™ MANIFOLDS (1500 to 6500 rpm)
The rpm runners will be higher volume and are intended for use in a higher rpm motor where runner velocity will be high enough to pack the cylinders properly. On a daily driver, the RPM will not be passing enough CFM to keep velocity up for good cylinder packing and the motor might run worse than it did with the stock manifold, particularly at lower rpm's.