https://www.thedrive.com/the-war-zone/3 ... per-bomber
The document covers a number of non-bomber variants, as well. Some of these make good sense, at least in principle, such as a tanker version, which would have been able to top up other fuel-hungry B-70s during missions. Robert Hopkins, an Air Force veteran, author, and contributor to the War Zone, with flying time on numerous C-135 variants, including KC-135 tankers, tweeted out "Not sure, however, if I'd want to try A/R [aerial refueling] at M=3.0 [Mach 3]" after seeing this new Air Force history. "Remember Pitch X Mach = VVI [Vertical Velocity Indicator], so a sneezing while refueling would be catastrophic!"
Frankly, the one variant that still makes some sense to me (in some sort of modern platform) is launching 200K pounds at mach 3 or so from 70K feet. But I don't think even stratolaunch is doing real well.