A couple of different things
The plane was rolled out on 7/8/7 (at least according to American reckoning).
The Bear was a turboprop that had HUGE fuel tanks. It wasn't capable of mid air refueling, which was its weak point. But it could fly from the USSR to most of the US, deliver its payload and return. It was flying at the time of the collapse of the Soviet Union.
The USAF experimented with Orion, but the "engine" was incredibly cranky and there were no solutions in sight at the time. I believe, however, that this was designed as a launch vehicle for rockets rather than and aircraft engine. Must look it up during my next test.
The USAF has been experimenting for years with replacement engines for the B52. The "fuel efficiency" of those almost 60 year old turbojets is terrible. The Air Force Times recently had an article about a B52 that was now being flown by the grandson of the original piolt. And who's father had also flown the same plane. That's how old those suckers are. And the Air Force says they are good for another 20 years or so.
Both the RR and the GE engines are within a miniscule amount in fuel efficiency. The PW engines weren't up to the task. But PW is getting lots of business on the small end, with several of the personal jets (Eclipse, Piper Mustang, etc).