The 2.5 inch system is wonderful if you have a turbo onboard.
2.25 for NA will do nicely
Have a read thru a performance exhaust book a d it will tell you what I said
Or look thru the Lukey Australia muffler web site , it will tell the same story
https://www.lukey.com.au/pages/exhaust-sizeGetting the right size exhaust is a definite must.
Make the exhaust diameter too big and the exhaust velocity decreases significantly.
Too small and it's too restrictive.
The stock NA exhaust diameter is 2 1/8th of inch.
Our can't buy that size at an exhaust shop.
Closest thing they have is 2.25 inch
If.you going to do this
Get extractor and then the fill system to replace the catalytic converter with 200 cell high flow