I haven't ever seen quantitative papers or books about this design decision, but qualitatively speaking it's more or less as you said. The B-36 specification heavily emphasized long range and thus cruise performance. As a rule a pusher configuration will be more efficient in cruise, subject to considerations like rotation on take off, which might force the pusher prop to be smaller diameter to clear the ground on rotation. However in B-36 case they found that pusher was definitely more efficient in cruise. Some early concepts leading to the B-36, and some wind tunnel models even, had push-pull nacelles or conventional tractor nacelles. but the designers believed pusher would win, and at least at the state of the art in wind tunnel testing at the time the tests proved them right.
The disadvantage of pusher is not so much that wing downwash will actually make it less efficient net, but the vibration considerations of uneven flow, not only wing downwash in cruise, but also the engine exhaust stream flowing through the prop. These were issues with the B-36 which had flight restrictions related to prop vibration. Also, besides the cruise configuration, the wing interaction issues become more serious with flaps down. Note in photo's of B-36's even fully extended flaps are continued right in front of the props. And also in low speed flight, the tractor prop helps generate lift which the pusher doens't to the same degree. And then there's more potential for FOD from stuff thrown into the props by the main gear; again see B-36 photo's: the main gear legs are within the radius of the inboard props.
Re: B-47, can't see how it could be compared to the B-36 in practically any way. The whole concept of its use was different, relying on friendly bases close to the USSR (many B-47's were homebased in CONUS, but practically speaking would need staging bases in Allied countries, even with aerial refueling). And it was an example of much more advanced state of art. The planes shared the J47 engine, but those were just an add on to the B-36, rather than the engine techology around which the B-47 was designed. And the B-47 was close enough in speed to enough of the Soviet interceptor force to make large scale B-47 nuclear raids essentially unstoppable (and there were lots of B-47's), even if groups of subsonic MiG's could intercept a single B-47 as they proved in certain RB-47 intrusions into Soviet territory or nearby. Although, even the B-36's capabilities were adequate to make the US nuclear deterrent credible v the USSR into the late 1950's. It's one thing to shoot down a bomber or cause a few % losses per sortie and make a conventional bombing campaign too costly. It's quite another to shoot down enough planes to make a nuclear attack's results tolerable: that was extremely difficult to do, requiring almost perfection for the defense and giving every advantage to the offense.
Joe