Go with the 5/16th spacer. It will give you more usable increases lower in the RMP band. The 1/2 spacer will give you a few more peak hp, but it's at the top of the RPM band that you will rarely use.
The MREV is really beneficial for 05-07 6MT Rev-up motors.
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Sean
Florida G35 Club OZOC Rotora
'03.5 Caribbean Blue 5at Sedan w/ a few mods, '04 Laser Red 6mt Vortech Coupe w/ many mods
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