[XT50033]

I find the 14' perfect. good luck

 

[Kiwi Rider]

I went down the same rabbit hole as you with my old CBR300. The shorty was too loud. I thought the 18" looked a little too long so I went with the 14" inch in carbon and it turned out to be bang on, but I did run it with the dB killer in.
I had a good run out of that pipe, just had to re-pack the muffling material after 20,000km of use.