This is a very hard question to answer for numerous reasons and one that will never be answered to everyone's satisfaction. Here are some things to consider and some problems that frequently come up when you're dealing with Lend Lease.
First off, significant Lend Lease aid was not felt until 1943. The Lend Lease that arrived before was nowhere near enough to make a decisive difference on how 1941 and 1942 turned out. There are some articles/arguments that have recently come out which attempt to argue that the Lend Lease tanks that did make it in 1941 played a decisive role in the defense of Moscow, but I don't believe they are conclusive enough (see the following article:
British “Lend-Lease” Tanks and the Battle for Moscow, November–December 1941—A Research Note).
Secondly, the immediate problems that come up when attempting to qualify Lend Lease are the following. Just quoting numbers of what was sent is not enough. One needs to account for what was sent,
when it arrived (and how much arrived), and
when it was actually incorporated into the Red Army and used in the field. Additionally, one has to keep in mind that the Soviets began to scale back production of certain things because they
knew they would receive them through Lend Lease. One example is trucks. The Soviets were producing practically none because they knew to expect them through Lend Lease, but that doesn't mean they couldn't produce more if they needed to. Many former truck producing factories were switched over to light tank production. Since the Red Army moved to relying on medium and heavy tanks, light tanks were something the Red Army could in theory do without or with less of. This type of analysis needs to be applied to
everything the Soviet Union received. Specifically, what they received, if it was not coming through Lend Lease what were the alternatives? Meaning could they produce it internally or import it from another state/country (England, Canada, etc.). The Soviet Union did not just receive Lend Lease from the US.
Finally, the Soviet Union participated in reverse Lend Lease, sending back materials to the US. All of the above is just the tip of the huge iceberg that studying Lend Lease means, it's simply impossible to account for all the variables.
EDIT: Not my words btw