Original post by AnathemeBy who? I have never ever heard that, and most definitely not regarding a language such as Russian.
OP, at the end of the day, doing Russian will make you stand out from all the other applicants, and it might just be what you need. You'll be that tad more original than most of the people who will have applied, and it will interest interviewers, as well as employers (who care), later on.
You could also have a chance to keep your Russian up at university as most unis have a language centre, so you could reach an alright level in it by the end of your degree and that would make you more employable. I wouldn't trust stats too much, maybe people get better grades in Russian because it's a subject they picked because of their interest in it, as opposed to trying to do Chemistry just to have a "serious" A-Level, as it may be the case.
If you have a degree in mind, for which you don't need Chemistry, go for Russian; if you decide to do Maths, Further Maths seems an obvious choice over Chemistry and Russian. For something like Economics, be careful to which university you'd rather apply, FM may be more useful. You won't know whichever would be easier if you don't try both at AS-Level, and I have a feeling the step so many languague student moan about will also be there from GCSE Russian and A-Level Russian. I don't know how much you've done, but if you haven't learnt about aspects, verbs of motion and participles, you may want to check those out, because they're a level far above cases (if you have, then you know what you're in for).