The plenum made a nice difference. I had the C&L plenum and 75mm throttle body on both my GT's, and just the trickflow and stock TB on the Mounty. In all three cases there was noticable improvement. On the Mustangs, I spent over $400 on each, but this time I only spent $110, and I'm just as happy. I think almost all of the gains come from the plenum and not the larger throttle body. If anything the slightly smaller throttle body might create an anti-reversion chamber, which would be good, but I'm not an engineer, just a guy with a lead foot. It's a no-brainer in my book - it's a difference you can feel for cheaper than something you might not feel (cold-air intake or cat-back exhaust]. Highly recommended.