IC piping size and S4 ECU question
 

I recently got another FMIC for my turbo'd na and it has 2.5" outlets as opposed to the ~2.0 stock ones. I was wondering if it was better to have more dynamic piping like turbo ->3" piping->2.5" piping->intercooler->3" piping (with one end smaller to mate up to intercooler)->TB or simply have 2.5" piping from turbo to the intercooler then 3" from intercooler to the TB.

Also (I did a search but didnt come across much), I was wondering if it was possible to swap a s4 turbo ecu in the place of my s4 n/a ecu. I know I don't have a knock sensor so that would be needed and a TII pressure sensor. However, would the N/A harness plug up to the turbo ECU? Is there anything else I am missing?

Thanks in advance everybody.