From what I remember from Hans' book, the Starfire was essentially a T-100 design and some of the first Starfires were T-100s that had been painted with the red tint. I may be wrong on this, but the bodies on the T-100s were laminated maple while the Starfire bodies were laminated mahogany - at least the ones I've seen. I've had two T-100s (my second one is a project in progress) and one Starfire III - I totally refinished the SF III and it was all mahogany. I think the SF II had the Adjustomatic bridge while the T-100 had the rosewood bridge. I'm also not sure if the very early Starfires (1960-61) shared any of the same pickups with the T-100. So, other that a couple minor things and the available colors, I don't think there was much difference between the two at all.
As far as how they felt and played - both had virtually the same neck dimensions and feel. The bodies were identical in shape and size. The weight was different because the SF III had the Bigsby, but I think the mahogany body was a bit heavier, too. My T-100 had a single Mickey Mouse pickup, and it sounded awesome! It was responsive enough to get a wide range of sounds, but it didn't like to be pushed to its max. I thought is provided a wonderful set of jazz tones - not too bright, but articulate. The SF III had the small humbuckers, and I really didn't care for them that much at all (of course, each of us has that magic sound in our head, and what may be perfect for me is gruesome to the next guy and vice verse). The SF III could get a greater variety of sounds and was of course more powerful. I kept the T-100 next to my computer and would constantly pick it up and play it while surfing - plus I used it mainly through a '68 Princeton Reverb. It was easily the best guitar I have ever owned in terms of its sound, feel, weight and how it fit my body (and personality). Of course, I sold it a few years ago.
I've never looked for another Starfire, but I've never stopped looking for another T-100. Fortunately, I found one - a basket case that I am rebuilding. This time, I won't let it get away from me! As far as your search, I think the SF II and the T-100D are essentially the same animal except for (as you indicate) cosmetics, pickups, and minor hardware. As such, either would be an excellent guitar to own. Good luck with your search!
Dean