Short summary of Lend-Lease to Soviets is like this in Wiki :
400,000 jeeps and trucks; 12,000 armored vehicles (including 7,000 tanks, about 1,386 of which were M3 Lees and 4,102 M4 Shermans);[27] 11,400 aircraft (4,719 of which were Bell P-39 Airacobras)[28] and 1.75 million tons of food.
Let's look at overall tank production in the war : Soviets 100k, USA 87k. I must also add that of 7k US tanks sent, only 4k was of Sherman Type, other were older tanks.
Aircraft production : USA 324k, Soviets 150k.
Just compare aircraft and tank production volume of Lend-Lease to overall production of Soviets. Yes, importance of Lend-Lease was mainly trucks + raw materials + food. I mentioned truck issue above, for raw materials and food, i accept that American help was quite important but i don't think Soviets would have lost without that help after 1943. Soviet didn't severely lack any material either ( like German lack of oil ) so that they collapse without US help.
Here is Lend-Lease volumes by year :
1941: 360,778t, of which 13,502t Persian Gulf, 193,229t Soviet Far East, 153,977t North Russia.
1942: 2,453,097t of which 705,259t Persian Gulf, 734,020 Soviet Far East, 949,711 North Russia, 64,107 Soviet Artic.
1943: 4,794,545t of which 1,606,979 Persian Gulf, 2,388,577 Soviet Far East, 681,043 North Russia, 117,946 Soviet Artic.
1944: 6,217,622t of which 1,788,864 Persian Gulf, 2,848,181 Soviet Far East, 1,452,775 North Russia, 127,802 Soviet Artic.
1945 3,673,819t (last shipments 20 Sept) of which: 44,513 Persian Gulf, 2,079,320 Soviet Far East, 726,725 North Russia, 680,723 Black Sea, 142,538 Soviet Artic.
So, we need to scale overall numbers listed in Wiki by those shipment tonnes to obtain approximate numbers shipped until Kursk.
And one final additional source for shipments :
http://peacecountry0.tripod.com/lendlse.htm