I'd be inclined to agree with discovery1 (about the Soviets only getting stronger), though in my games I usually wait until 42 before launching Barbarossa.

The time can be used to take the British isles, establish a fortified line in Poland to prevent the Russians from advancing in case the attack fails, and establishing a massive, and I mean massive army.

Personally, I usually attack with, at the least, 6 tank armies (each tank army being 6 divisions, each with an appropriate mobile attachment), 3 armies (9 divisions, 1 HQ, 2 tank, 6 mechanized, all outfitted with attachments for mobility) and a whole lot of holding corps (this can take any form you like, but in my case they are usually comprised of 3 motorized divisions with artillery, at and engineer attachments). Also, lots and lots of air support. Naval supremacy can work wonders coupled with sufficient Marines and Paratroopers, as you will likely force the Soviets to split their troops even more. Missiles are good, too for bombing those industrial centres, especially after the transfer of industry event fires (their industry will get concentrated around the Urals, if you can hit those, their industry will take a nose-dive).

The advance will be quick enough with such a composition of land forces, if you make sure that there are no holes in your line. The holding corps are generally not going to stop a Soviet counter-attack, but will slow one down long enough for your hitters to get into position to cut them off. They'll also be useful for baiting the Soviets into stretching their forces thin. Once you get into Russia proper the Soviets will begin leaving holes in their defensive lines. Also, make sure not to drift too far north with your troop concentration (a mistake I usually make, leaving me with 80% of my forces in the forests and swamps around Leningrad).

The only problem with this strategy is oil, you'll need a lot of it, and by a lot I mean a whole lot. The mid East must be yours (I use 1941 for this), and you'll need to import from Romania and all countries with access to any oil. Also, the Baku oil fields in Azerbeijan will need to be a priority for the invasion. During the invasion, keep your fleet in ports, they'll drain your oil something fierce.

The up side is that once you get to the Urals, you'll have an invulnerable front line, and by the time the USSR is gone, you'll have such an army that you can wipe the floor with the USA, Japan and any other nation that gets in your way ... at the same time.