Survival. Hitler and Stalin were already in bed with each other in the eyes of the West, declaring war on the USSR as well as Nazi Germany would just tuck the quilt over them and give them a teddy bear.
Such differing ideologies would not stay friendly forever, and I'd wager that the west knew that sooner or later there would be a falling out between them.
Tater, your victory plans make sense but where do you factor the Soviet Union into it...I'm not so sure that Stalin would be willing to let the Nazis expand infinitely, although the longer he waited before striking the Germans the more powerful the Germans would have become.
I'd also wager eventual US involvement, bear in mind that by 1941 US destroyers are actively hunting uboats outside of US territorial waters. The lend-lease act of March '41 gave Roosevelt the ability to throw as much material at Britain as he could get away with and only the uboats could stop them. Bear in mind that although the uboat war was still tough for the UK, it was swinging slightly against Germany up until the US entered the war officially and the second Happy Times came about before the US got around to listening to British advice on how to run a convoy system. So, perhaps if US involvement came later in the war because Japan was focusing on the UK and Germany was in the Middle East instead of in the Soviet Union, it perhaps could have swung the Uboat war a bit more in the allies favour as the shipping lane opportunities dried up. It would, of course, also prolong the war, so you have a greater chance of equipment like the Type XXI and Me-262 making it into greater production...but I do ponder how much of an effect they would have had.
The long and the short of it though, it all boils down to the Soviet Union. Once they are fully mobilised, Germany needs to be as ready as it can be to fight off the hordes and then push back to Moscow. However, the Soviets have the advantage of being able to set the timetable of the war if they attacked first.
Long post...and completely off the original topic so I shall draw it to a close here...but I do enjoy alternate history and exploring different outcomes.
