downpipe 63/70/76mm difference?

[unknown_user]

Like subject says, what is the power difference?Curently I am runing stock setup, but now I decided to build custom exhaust.But I don't want that the car will be to loud and noisy inside.
I thinking on new setup:

custom 70 or 76 mm downpipes without cats with stock middle silencer and rear silencer?Is that combination too loud?Opinions?What power gain could i expect?
Car is curently runing on SKN map.[url]http://www.skn-tuning.de/en/produkt.htm ... &id=532676&[/url]

Thank you.

[Rick_RS4]

Larger bore will give better flow but will be louder. If you want optimal performance you need larger bore. Depends what your after. I'm not sure what optimal bore size is for your engine but decat will make it louder again however the standard centre and rear will quieten it down