Basically, what everyone else has said. Status timing is just to get the engine /running/; to get it running /well/ requires adjustments.
Each pump is slightly different, and pop pressures do affect it by a significant amount. A couple of degrees is the difference between a clattery hard-to-rev engine, and a smoother, more powerful and more fuel efficient engine.
Also, as far as I'm concerned, the nominal degrees(8 degrees NA, 6 degrees with a turbo) are good if you've got a new pump.
If you are reusing a worn pump, well, it's a /start/ at best. Mainly because the internal timing piston wears and will give you a different timing curve; you can work around it to some extent by messing with the light load advance cam, and adjusting base timing based on how the engine runs.
The problem is that the actual timing curve is a 3 factor curve involving RPM, fueling, and throttle position(due to the light load cam)... and once the internals wear a bit, it changes unpredictably.
In your case, as you aren't replacing your pump, I suggest that after you time it to 6 or 8 degrees, see how it runs. Then advance it 2 degrees and see how it does. Better or worse. If worse, retard 2 degrees and keep doing this until it feels the 'best'.
Note that you may end up with something where it feels "good" in the low end, but "off"(either clattery or smokes white) at the high end. Or vice versa.
I always aim for the mid range to top(loaded, accelerating) to feel the best, then adjust the light load advance cam to fix the low end.