Doing a side-by-side comparison of these two. The Yeti is much more intense. Extreme bitterness, dark fruit, sweet chocolate, coffee, hoppy. The Old Rasputin is much less intense. Coffee, chocolate, little to no hop flavor, but some hop aroma. It has a much cleaner taste to it (I assume because of the yeast and/or fermentation temp). Between the two I'm gonna have to pick the yeti as my favorite. When it comes to imperial stouts, the more intense the better. I still consider Oskar Blues Ten Fidy to be my favorite imperial stout still. I haven't found anything better yet.
I'm noticing that great divides beers all have the same aroma. I don't think it's hops, it's may be their house yeast character, but I'm not sure. It's kinda weird though...