On the track or any time you're at speed it won't make a much of a difference because air is forced in the front air dam, past the engine and mostly out the transmission tunnel with some going out past the steering arms and overpipe. The problem is at idle everything in the compartment heat soaks immediately because the upper half of the engine bay is sealed.
The other problem is uncoated headers radiate heat directly at head gaskets, front engine cover gasket, thermostat gasket, gasket sealant, etc so down the road you or the unsuspecting next owner has to tear the whole engine out to replace those. Uncoated catted headers would be the worse.
When you get OFT or custom tune, regardless of what headers you have, adjust your radiator fans to come on at idle, so you avoid unnecessarily heat soaking everything in the engine bay by an extra 20C.
http://www.ft86club.com/forums/showthread.php?t=64731
Tomei is a cleaner install, at an extra cost of about $300 and a couple days back and forward to coaters (850 + 150 OP + 250 coating).
PSR:
