First of all, this is a great theme and thank you very much for it.
This is meant to be more of a note for others that might be trying to track down the same issue.
Out of the box, I was noticed that .col-620 was actually displaying at 605px and .col-300 was displaying at 293px (assume the same percentage differences for other columns).
The css uses percentages based on a 960 grid for column widths, which is great, but the wrapper is 960px wide with 20px of padding on the left and the right and a border. This only leaves a content area of 918px versus the 940px that a 960 grid expects. Having the outside container a little narrower than expected, makes all the columns a little narrower than expected.
Changing the padding on #wrapper to have left and right padding of 10px instead of 20px, and removing the border on it made the columns display at the actual pixel widths expected.