Check out the plenum showdown by modulardepot.com:
Part 1 with 70mm TBs -
http://www.modulardepot.com/?show=articlesdet&aid=30
Part 2 with 75mm TBs -
http://www.modulardepot.com/?show=articlesdet&aid=38
The test mule was an 03 GT with just full exhaust and pulleys.
Also note since these tests were run, Accufab has come out with a newer plenum that takes advantage of the 75mm TB size.
My advice? The Accufab 75 mm TB and Accufab plenum. You won't go wrong with Accufab - quality stuff!
A TB alone won't give you much power by itself...