I've tried A LOT of pre-mufflers / active pre-muffler / stock mufflers / modified stock muffler / sport mufflers / stock heat exchanger and header permutations. 1 in / 1 out and 2 in / 1 out.
I went from this...
To this...
...in the name of extracting every last HP out of a 3.4 liter, single plug, 964 cam, Motronic build AND looking for a particular sound. It's a VERY expensive last mile / step.
Everyone's Price / Value / Happiness matrix is different, but for my $, as a general rule of thumb, I'd stick with stock HEs and some combination of cat bypass / resonated / active pre-muffler + sport muffler on anything up to a 3.4 liter single plug Motronic motor and reserve the header / two-in muffler setups for 3.5 liter+, twin plug, non-Motronic motors.