T6 exhaust imo sucks balls, I would get CPI. Not much of a price difference if any.
What fuel do you wanna run?
With the porting you mentioned you will see minimal gains if any hp wise. If your staying pump fuel look into 21cc domes from a site sponsor, they all run similar bandwidth,angle and will run better than a off the shelf prodesign.
With the porting you mentioned and better pipes start around 320 main 27.5 pilots