Hi Spud,
You're absolutely right about the value of US (and UK) aid to the Soviets during World War Two keeping them from losing. Without Lend-Lease, the Red Army may well not have won, and certainly would not have been the superb military force it became in 1944-1945. The supplies of US-made planes, tanks and small arms are well know, but perhaps the most important exports to the Soviets from the US were trucks, jeeps and food. Yes, food. American k-rations, designed to last forever, filled the stomachs of the Soviet soldiers while they advanced westwards. This, while much of the Soviet Union was near starvation (the loss of the Soviet "food basket", the Ukraine, was particularly problematic.)
But even if those 75% of of Nazi war dead had come at the hands of UK-US soldiers rather than Russians, as you suggest, this would have meant one hell of a lot more dead Yanks and Limeys. The Russians got our steel, bullets, guns, etc. They gave back their blood.