Jane, the Vulcan time to 45k was about 9 minutes at full chat. At 5000 fpm it would be at height some 60-70 nm from take-off. A B58 at a higher climb rate might have only gained 30 nm high altitude cruise - insignifcant I suggest.
ROA, correct.
Supersonic cruise all the way? I don't think so. The Force d'Frappe had a similar capability which was as I described - high-subsonic with a supersonic target penetration.
A DID report in the mid-60s analysed an SA3 (I think) engagement with a headon target at high subsonic speed - it could have been against the B58 or the upcoming FB111. It calculated the number of shots that a battery could fire - single shot - as the aircraft approached, overflew, and departed. I cannot remember exactly if it was the SA3 on a low level engagement or SA2 on a high level one. It was before the multiple SA2 launchers were developed.
Pentration of the Moscow SAM belt was a special case and high speed, non-manoeuvering penetration would probably have worked.
Finally, on the Bomb Comps the B58 sortie was IIRO 6 Hours.