Never played Thief, but I logged a lot of hours in Unreal, 1998. I was (and still am) amazed at how full-featured the software renderer was. I always wished I could peek at the code behind it.
If memory serves, the only thing my 3dfx Voodoo3 could do that software-only mode could not was surface reflections. Maybe something with colored lighting too, it's been a long time. Point is, it was a decent enough substitute for dedicated graphics hardware.
S 3 X Y
The C didn’t fit that, nor would a 2. Unless he’s aiming for a lineup of products that has you seeing someone next Tuesday.