Re: Trademarks, your experience shows how truly subjective Trademarks are...
Not Legal Advice- May not know all the facts- There may be other particulars to your situation (including the exact names involved) that could alter the following...
I agree with Kaitlyn that bar and bar and grill are generic names. However, when examining a Trademar, I believe that the commercial impression of the marks as a whole would be what determines confisingly similar (and this infringing).
First, a question... What is "Moscow Troika"? Is Troika a region/part of the city of Moscow? A type of food? And are there other bars or restaurants in your city with Moscow in the title? i.e., The Moscow Cuisine, The Moscow Eatery, Bar Moscow? etc? If there are one or two others that have apparently coexisted with the Moscow Troika Bar, then you may be alright.
Digging in memory, restaurants with confusingly similar names have been given at least a range of 20-25 miles Radius (not re: Federal Registered marks, but common law (unregistered) marks). Thus, to have a restaurant with a confiusingly similar name within that range (and thus the same geographic area of the existing mark) would be infringement. Thus, if you live in a larger city, and the restaurants may be found in the same yellow pages, or be advertised on the same radio station, I would say that a range of greater than 25 miles away could still be within a problematic range for the trademarks, especially where "The Moscow Troika Bar" is well-known in that community.
Just curious- Why did you select Moscow Bar and Grill for your name?
Regarding confusion and looking at the marks as a whole, could the existence of 'Troika' in the existing mark be considered a dominant part of that name? If so, leaving it out in your proposed name may be acceptable. If there are other marks in your area with Moscow in the name for restaurants/bars, then the mark itself may be considered weak, and thus you may be ok. However, if this is the only restaurant/food/bar name within 200 miles with any inkling of 'Moscow' in the name, then you may be close enough to be confusingly similar.
Really depends on the specifics. If a consumer heard your commercial for "The Moscow Bar and Grill" and knew of the prior "Moscow Troika Bar", might they think (from memory) that the current commercial might be that of "Moscow Troika Bar", that they've heard from friends was so great? Or might they think that you are otherwise affiliated with "Moscow Troika Bar"?