I wasnt aware of any serious contacts after Kursk, but its not impossible considering the shadowy nature of negotiations during a war.
There were contacts throughout 1942 as well, though. I think the best times for Germany to accept a deal would be late 1941 or summer 42, obviously, since its when they have the most momentum and can extract the most concessions.
Lets say the deal gives Germany the Baltics, Bielorussia, and most of the Ukraine, including Kiev and Crimea. The most immediate considerations include whether the Western allies feel so betrayed that they cut off lend-lease, or whether they accept Stalin's line, which would be that his country was on the verge of collapse, that this is a temporary truce, and that he needs arms to fight again two years down the line. I'd err on the side that the US would reluctantly continue to provide aid whilst pushing for renewed hostilities.
The second question is; is America in the war yet. If it happens in 41, before Pearl Harbor, its back to Britain vs Germany, and Hitler is less likely to want to declare war on the US if he believes that the blow he delivered to the Soviets (who look militarily incompetant at best) might encourage London to negociate. Whilst I really doubt it, unless its paired with great victories in the Mediteranean, its very much how Hitler thought. He produced tons of documents and citations regarding how defeating the Soviets was critical to bring Britain to the peace table. I believe he was mostly rationalizing his burning desire for an eastern war, and wanted to sell this idea despite the German fear of a two-front war.
The third question is how long this peace lasts. Though the Soviet contacts were very real if ill-documented, it was plain for all this was a truce and not a lasting peace. There's an Hitler quote regarding this, as well, in which he said to his generals that if he signed a truce, he would "want to attack the Soviet Union again the next day". The Germans saw the Soviet ouvertures as a way to gain time and improve the battle lines, for the most part, so they didnt want to sacrifice much land with this in mind.
A fourth question is PoWs. A 41/42 truce means that Germany has millions (6-8 of them!) of Soviet PoWs whilst Moscow has only thousands of German prisonners. Releasing them is essentially a no-go for Berlin, as they represent too much combat power. Fortunately for our hypothetical truce, Stalin apparently never asked for them, said they were traitors to the motherland, and said to his generals that they were all to be shot (!) if they were returned because they all surrendered without authorization. This was the Soviet SOP during most of the war for any recaptured prisoners. Stalin's orders were merciless and nobody dared disobey - though it admittedly helped discourage his troops from surrendering as well. I'm guessing that the most likely scenario is no prisoner exchange. But I have to imagine for a minute what would happen if the Soviets tried to execute immense amounts of returning prisoners like this. I just can't imagine how much trauma an holocaust-sized shooting squad would generate for the country, nor that Stalin would survive that order long.
So, my guess on all this?
A 1941 truce is initially good for Germany, which has a much less rigorous winter-41 experience, and can temporarily focus on Britain again. However sometime in 42, Roosevelt gets a DoW against Germany even if Hitler's DoW is butterflied away. From that point on, things are only marginally better for the Axis. Lend-lease shipments resume to the Soviets, and are attacked by u-boats just as much as before, which can provide the casus-belli to resume hostilities once Stalin feels ready. Since this was his plan all along, in late spring 1943, he WILL attack again (unless the western allies are doing incredibly poorly), though German positions and resistance will be much stiffer than in OTL. Also, in the meantime, vast available German ressources could have lead to the fall of Suez in 42. However, since by then America is at war, this doesn't trigger Churchill's fall, and Egypt will be retaken soon after. The Axis is thus still likely to lose in 45, probably a few months late.
What this can open up, as a low-probability scenario, is the possibility that Hitler can use the psychological impact of a victorious peace in the East to encourage the UK to come to terms pre US-entry. With Churchill in power, its as unlikely as ever, but there would be greater pressure than before to consider it. Coupled with the right concessions in the west, who knows. Theres certainly going to be a level of gloom and doom in London that has never been seen before, with Hitler lording from Brest to Rostov. It could open opportunities that we tend to dismiss since they never arose in OTL. I read a book in French with another quote attributed to Hitler regarding this. One of his diplomats was suggesting that a deal with either the Soviets or the Allies could be leveraged to bring the other party to peace as well, and he is said to have replied "This is all politics. And politics bore me now. I don't do politics anymore."
With that kind of mindset from Germany's leader, getting anything worthwhile out of a truce is really a long shot.
Finally, back to lend-lease; if the US considers Stalin's truce too much of a betrayal to grant lend-lease, theres a strong possibility that the USSR would not recover well enough to mount an offensive against the Nazis again, period. Many strategic resources essential to Russia were in the western territories that would be lost in this land-swap, and lend-lease filled critical gaps that would have brought Soviet industry to it's knees in 42/43. The value of Ukraine, Bielorussia and the Baltics cannot be understated from a Russian POV. There are thus viable scenarios to consider there.