Hi Gimmy;
FWIW: I was just working on a customer PDF issue this AM where I generated a few PDF's using various mechanisms for testing with the customer's DWO. Surprisingly enough, the NativePDF way produced the smallest PDF. So I suspect that you might need to evaluate the PostScript vs NativePDF approach for each PDF. Depending on the type, size, complexity, security, compliance standard, etc of information to be included in your PDF(s) - the sizes can vary quite a bit.
My Tests ...
HTH
Regards ... Chris