Shaner or Bauer are 2 guys that do good work. I had mine ported by Bauer, the primary reason I decided on Bauer is because (at the time) he offered powerder coating too. The port & polish work was done well and the area around the breather connector was epoxied & drilled out to smooth out the intake side of the TB better. On my bolt-on motor, probably not much improvement in the RWHP department, but I did notice improved throttle response, especially once the motor got up on the cam and the hammer is put down. Consider this mod as part of your overall package, and not a significant RWHP improvement all by itself.
I test C5 ported TBs for Bauer Racing. My basically stock '97 A4 still idles at 550 with the TB ported especially for an automatic. His M6 porting is slightly different, as they don't seem as sensitive at idle. Currently mine is coated bright red to match the lettering on the fuel rail covers. I like the semi-gloss black however.
Back when I was looking for a ported TB for my SS, I did some reasearch and found Bauer to be one of the most reputable.....after placing my order with him and receiving the part within a week I knew i had made the right decision. Excellent service, fast, and an awesome product. Bret does some wicked work on TB's.