Some considerations from another side.
1. It's pity to see such a topic. SU, US and GB were good allies during the WWII, and nobody in the Stalin's mob was really planning to move further westward after Berlin was taken. Yes, in some memoirs of the Stalin's multi-star generals it was mentioned that some commanders were raising such a topic, but these were rather chats over vodka after some unintentional friendly fire took place in the last days of war.
2. Stalin had a clear plan regarding Europe. First, to crack down Hitler completely and denazify Germany. No "side trips" were planned. Second, to extend his influence and control over the territories liberated from the nazis by SU. Note that puppet governments were later put in place only in the countries that were "on the march mainstream". It seemed rather fair at that time: hundreds of thousands lives were left in Eastern Europe. Note also that countries alongside the route, such as e.g. Finland and Norway ( north) and Austria (south), were not included in the pro-Soviet block though many soldier lives were left there as well.
3. "Great three" (US, UK and SU) have just agreed (in Yalta/Crimea in Feb 1945 and later in Potsdam) on the principles of a new world order after WWII. Stalin seemed to be satisfied with the agreements reached. What the hell would he turn the guns towards yesterday's colleagues?
4. OK, forgetting the above 1-3, and taking an abstraction of a military conflict, it's better operate with numbers. First, leaving only UK vs SU (taking US out)makes no sense. SU had three times more troops, planes, tanks and self-propelled artillery, etc. than GB. Soldiers and officers had extremely rich combat experience in air and land ops (Navy is not the case here). Thus, no chances. Let's now "take US in". US had comparable (to SU) armed forces (e.g. both had about 11+ mln army), but only a minor part of them were in the European theatre. Anyway, still a serious threat to SU. In my opinion, SU would anyway reach the Atlantic, but would then have to face regular bomber attacks from many directions and I can hardly predict the result as it would be a very long conflict (like a GB vs Germany over the Channel for some 6 years). Taking a longer period into consideration (when A- and H-stuff appeared), it is well-known that SU could hardly adequately reply to US plans like "dropshot" until late 50's.