Pungent grey/blue smoke, right at startup only is indicative of valve guides being worn. Oil is seeping down between valve stem and valve guide and collecting in the combustion chamber, and being burnt away when you start the engine.
The same smoke whenever you put the foot in indicates oil entering the combustion chamger whenever you have higher oil pressure. Could be your oil control ringe being worn, or another oil leak into the inlet runner somewhere else, but it's unlikeley.
Usually if there is no / less smoke at idle and more at a 2000 rpm it's oil rings.
For your oil rings to be worn, you can bet your bottom dollar that other things are worn too. If I was in your shoes, I would get a trustworthy mechanic to compression test all 6 cylinders and report back the pressures to you. 150-155KPA is ideal. Under 130 Will be indicative of cylinder leakdown (getting old) and less than 120KPA means full rebuild time.
That being said, 250000 and 155KPA occurs often with the Ecotecs. You can't kill 'em.
the compression test will narrow this down, if just one or 2 have lost compression you could be looking at damage from something else, rather than wear.
Oh and surging / pulling at idle rpm with the foot on the brake ? Vacuum leak would be my first thought, check hoses and lines from Throttlebody to ...wherever it is they go. Actually there is a mild surge that occurs in mine that I put down to the tune I got with the throttlebody. Once every 30 seconds at idle it sort 'of clears its throat' with a rev up to about 1000rpm before dropping back to 700 rpm.
