Wow, sounds awesome. I'm considering St.Petersburg and/or Moscow for New Year.
Did you end up taking the train from Paris to Moscow?
No. Flew from Paris to Moscow and back from St. P to Paris. Although I would LOVE to do that one day. I love train travel.
Why and/or? If you're going all that way, you might as well do both. They are very different and both worth visiting. But if you're in Europe you probably have more opportunities to visit them because you're closer.