Well, to put this line of speculation to rest, my UFO is staying !!!! And won't be upstaged by an SC anytime soon. The 1/8" metal drill bit (with a slight bit of extra circumfrential reaming) made the perfect horizontal, level hole to hold the probe just above the stirring arms. (Okay, one arm bumps just very slightly as it goes underneath, but not enough to stop it.)
If/as/when my UFO takes a powder, I will revisit the pros and cons of the two different popper bases. For now I'm finally getting the hang of it.
Yesterday I set the TO at 410 with the UFO heater on until the probe read 200. Then I poured the beans in, turned the TO UFO off (edit: oops, I didn't turn the TO off, I turned the UFO off), and sailed smoothly up to 300 in 4 1/2 minutes (158, 185, 204, 233, 248, 266, 294, 298). From there to FC1C (edit: First Crack should be written 1C) took another 6 minutes (323, 323, 330, 338, 348, 359, 359, 374, 384, 395, 402). And I dumped the roast 2 1/2 minutes later (410, 413, 420, 420, 435).
I was using BW's "test beans", but I was really happy to see that starting with the lower "charge" temp made a huge difference, and I think I am finally on the way towards ..... home roasted nirvanha !!! or at least towards beans I don't have to throw away !!!!
Susan