I did maths, chemistry, biology and classics to A2 and I can honestly say that I regret not dropping classics after AS.
Don't jeopardise your overall grades for the sake of impressing universities. To do a subject because you enjoy it is quite silly as well. If I like classical history I can just study it as a hobby, I could have read the Aeneid now in my three months of summer holiday instead of the night before the exam (when it also clashed with maths)!
Be wary though, I had some really hard working friends who did only maths/chem/bio at A2 and they surprisingly didn't get straight A grades. It all comes down to your willpower and how hard you study.