Thanks for the comprehensive details. I have studied both Sherline and Taig web sites and I am inclined to get the Sherline, because it comes in metric, has a DC motor OOB so I can use it right out of the box without doing any modification.
About the biggest size I would turn, it looks like the wheels are more in the range of 35 - 50 mm in diameter (outer) so it should not be a problem. Now, if only I can find some tips & tricks about how to turn wheel rims and how to drill the nipple holes accurately.