Makes sense, thanks. I guess this would also explain the tempdb Transaction Log 'hangover' I've got, almost .5 GB of Used space that won't release. Now I can be certain it is the unfinished transaction I killed about halfway through the Sort. Total table size is 550 MB. I'll consider restarting the instance this weekend to free that up.

What is surprising to me is the use of the tempdb Transaction Log for the sort. That's the part I want to really understand, so I'm going to try to spit back a summary of your description as I understand it. Corrections would be welcomed. Here goes:

The ORDER BY on the unindexed column caused the table to be written to tempdb (data) as a heap, and this write is recorded in the tempdb Transaction Log, just like any row creation event in a standard database table?

Interesting. I have to say I've never thought too hard about it but it's clear that tempdb utilizes the fundamentals of the Storage Engine and Transaction Manager just like any other DB.

Thanks again for your brain dump. Much appreciated!