In the latter scenario, the US, not russia is the more important ally due to thier industrial capabilities, replacing shipping tonnage during the BoA was important, in the end it was a battle they lost on tehcnical merits as the RN became adept at sub hunting, submarine technology would not be mature until nuclear reactors became the norm, only then could huge numbers make a massively telling difference.
On the former, it's just very difficult to see how Germany manages to produce enough stuff in a short period of time. Bare in mind that the gemrans did not adopt a proper war economy until 43/44. It's very liekly that they owuld ahve sought an armistice rather than f**k their economy - they'd built their entire armed forces on the idea of short wars on land. They just didn't ahve the capacity for taking us on, on our own patch. I think you would have seen some form of cold war between the two later. However, Hitler was always going to go east.
It's just worng to imagine that the events of 1940/1941 had no baring on the overall result, indeed, not only did they save the UK, but continued British resistance delayed the start of Barbarrosa to the point where eventually the Germans ran out of good weather and got bogged down outside of Moscow.