I recently added the Cobb Stage 1 93 tune to my 2013 BS, which only had a Soul Valvetronic exhaust as a non-stock "performance" mod.
The Soul exhaust is magnificent because you can turn the sound UP or DOWN using your HomeLink buttons. You can go from mild sound to wild sound just by pressing a button, like PSE except wilder.
According to the Cobb maps, the Stage 1 93 tune adds about 27HP and 18 FP's to the Boxster S. The exhaust is a sound option, so no power gains are expected without headers.
Historical data shows the 981 BS was originally rated by Porsche at 4.8 seconds in the 0-60 run, but 4.5/4.6 is probably more accurate, Porsche is not known to fudge this number.
The Cobb tune & Soul exhaust combination produced an electronically timed 3.85 second 0-60 run in 70F sunshine today, with the top up. Put the top and windows down and the car slowed to 3.99 seconds.
I really didn't expect to see 3's in the outcome. I would have been pleased with 4.0 to 4.2.
Props to Cobb in concert with Soul for these results.
(Sorry that I didn't capture baseline data.)