Interesting stuff. Beria was dead right about Churchill, who was absolutely the key figure in holding the line against the Axis in the early war years. He made some specific errors in strategy at times, but his overall psychological effect on the British will to fight was incalculable. He was definitely THE thorn in the side of the Axis.
I wouldn't doubt that Stalin had thoughts about moving west in 1945. On the other side of the line, Patton had similar plans to move east and drive the Russians right out of western Europe and even to the gates of Moscow. He was also hoping to immediately reform the German Wermacht veterans under western Allied command and use them to help fight the Russians. Had this been done, the Germans would have fought more than willingly beside the western Allies. They had been hoping for such an alliance against the Soviets for some time, but could find no political way to arrange it as long as Hitler was alive.
Patton's superiors were so rattled by his bellicose talk of attacking the Russians that they cashiered him to other duties as quickly as possible...putting him where he could "do no harm", so to speak.
So there were strong ideas on both sides (in various quarters) for continuing that war into a Red Star vs White Star conflict.
However, I don't think the Russians would have found it easy going, even had there been no atom bomb. Their weaponry on the whole was not as advanced, particularly their aircraft. In my opinion, based on decades of wargaming, the Allied Air Forces would have made hash out of them, and the American and British heavy bomber fleets would have bombed out most of their industrial centres in a year. Russia was getting tired by 1945, feeling the beginning of a pinch in manpower, and much of their country was devastated, while the USA was undamaged and producing arms at an unprecedented rate.
The Russian troops in the field, on the other hand, were filled with confidence after their victory over the Germans, so I'm not surprised they felt optimistic.
The Germans would have volunteered en masse to re-enlist in the Allied forces, and would have been well supplied for a change, with plenty of new equipment...and they would have fought like hell against the Russians.
Allied air power would have been the crucial factor, as it was against the Germans. They were the most skillful and experienced army on the ground in '44 and '45, but Allied air supremacy hamstrung them on every occasion, pinning them down, cutting their supply lines, and destroying their panzers. I expect the same would have happened to the Russians.
It would have been a very bloody and protracted business, though. No cakewalk. Not for either side.
For all I know you may be right that the Russians had the strenght to win in western Europe in '45, but I doubt it. They would probably have fought to an eventual stalemate somewhere in the middle of Eastern Europe.
And another 20 million would have died. Good thing it didn't happen.