Walbut - Note all the comments about the Bucc's relative sloth in the big TSR2 history document, talking about a max low level speed of 0.85.
On the other hand, you're not going to sustain a speed much faster than that (.05-.10 Mach faster, tops) and the faster you go, the harder you're going to work to follow terrain. And the difference is more marked as you get into TA rather than pure TF. From talking to Rafale people, they seem to do low-level at 550 kt, which is about 0.85 on the deck.
However, it was really only the RN and the USN which managed to resist the lure of supersonic speed (Bucc, A-4 and A-6). Probably for the same reason - supersonic, A/G-payload and long range off a carrier could be done, but at vast cost and not in a very flexible manner.
Personal view: the Bucc could have done the RAF strike mission at least as well as the Tonka, which added a lot of complexity in order to cover the interceptor role (which eventually involved a lot of Sturm und Drang and massive redesign. Or did the 800 kt capability add a lot to the Tonka's capabilities? I am truly all ears and would be ready to be corrected.
(At least the RAF didn't try to make a low-level strategic bomber do 2.2, and then finally field the bu$$er in a configuration that was to all intents and purposes subsonic.)