I ordered a Diamond Eye 4” straight exhaust with 3” downpipe from Summit Racing. They accidentally sent the 5” exhaust straight kit…

After watching and listening and reading about either or exhaust size, it seems there is not much of a difference except sound…

I read that the 4” is better because some back pressure is needed for the turbo to spool faster and I also read that the 5” is better because you don’t want back pressure at all to reduce the chance of head gasket failure…

So my question is…

With all the mixed matched info out there….

Which will be better performance and longevity wise? The 5” or 4”?

Any more clarification will be helpful.