JasonB,
I must beg to differ slightly on the .125mm difference in the diameter. That translates to less than .005 inch. In practice, with the arbor nut and flanges tightened down, I suspect that it will rotate even less than that off centre. As long as the arbor is concentric, the back flange is machined accurately and the blade is flat; then the (less than) .005 inch off centre should, in practice, have negligible effect. Any of the other factors (arbor runout, inaccurate [less than flat] flange, warped blade) should have more effect than the .005 inch on the blade bore. In fact, I'm sure having a couple of chipped or replaced teeth will likely cause it to be more out of balance.
Yes, ideally a 5/8" is better than 16mm. But if one is able to have a better choice of blade by going with the 16mm, then it should cause no problems in practice.
I agree with what you're saying about reducing bushes, I have a number of 30mm bore blades with reducing bushes. I also agree about using full kerf blades (though I do have a couple of decent thin-kerf blades).
Brad