On a one for one basis it's impossible to compare because of many additional factors. You correctly note that this is irrelevant because in reality a tank fights as part of an army. You then however completely ignore the particularities of the situation. We (Russian) currently have ~300 (slightly less then ) T-90A, and maybe another ~120 T-90 with another ~250 T-90A to be delivered in the next few years. These tanks form only a fraction of our total armored forces. The majority remains with the T-72, with the T-80in second place. Even if the 2015 state armaments program is fulfilled fully in regards to the T-90A, only 1400 will be produced. And that program has long since become unfulfillable. Not to mention that individual training is likely to be worse, and air support is certainly going to be lacking. Finally how do you propose to deliver our non-existent T-90As to East Germany?
Realistically there is no situation currently where large scale armored warfare between us and NATO is possible. Not to mention the Russian military doctrine (last I read it) clearly states that Russia has a first-use policy on nuclear weapons.
2015 is a long way to go still. How can you be so sure that it won't happen? I can understand the current Russian economy may not be able to handle war preparations as much as their Soviet predecessor. However, we have six years between 2009 and 2015. Anything could happen.
Who knows? Maybe the Arab oil-wells may deplete faster than expected. A civil war or dissent could break out in Saudi Arabia. With nowhere else to get oil, the Westerners may need to rely on Russian fuel instead. As I see it, Russia is one of the major energy powers in the world.
Let's also remember that the T90 was more of a stop-gap measure until Russia can make the projected so-called T95. All previous tanks will cease to be built and whatever remains will not be modernized. That's why it's essentially an up-gunned and up-armored T72B that provides similar performance to T80 models above the U standard.
There is no point denying that it is clear the Russians have a disadvantage when it comes to quantity terms for the T90. I agree, too few of these tanks won't be able to make a difference.
And, Central Germany was just a reference. They are not the only ones with open plains in the world. Central Germany was just an example of where the T90 would operate best. I'll admit that the T90 would greatly suffer in cities like Berlin, like any other tank would.
And, I think in any case, the only reason to use a nuke would be Mutually Assured Destruction. You can't use a nuke on a strategic target, that would complicate things a lot. But then again, I really don't know how Russian tacticians think, but they can't be that crazy to use nukes right? They'd suffer as much as their enemies.
You are also right about a conventional war breaking out. And the air support thing, well Russia's got to think of a way to get there. But, as I hear the S300 and S400 are quite capable as AA missile systems.