When I use my Paasche Millenium, I only use the polished needles. The difference is absolutely worth the extra cost per needle.
I believe that the "polished" needles simply improved consistency for me... By that I mean that when I pull back on the trigger, I get a smooth, even reaction. With the "stock" needles, it was less predictable.
Let me know if you need more info.
Later,
Tim