They give out their standard offer to anyone with predicted grades that are high enough (see their faq http://www2.warwick.ac.uk/fac/sci/maths/admissions/ug/faqs/#ansb1 ). So I don't think additional further maths would make any difference to this, and you'd probably still receive the same standard offer that they give to everyone else.
However they do say that they like FP and M modules and that doing well in them would increase your chances of being let in if you narrowly miss your offer. So you would presumably have more of those which is good.