It doesn't really matter. If you're just starting sixth form then perhaps chemistry would be more useful but if you've already done your as levels it doesn't matter much and shouldn't be a disadvantage to your application
For most university courses the 4th A level does not matter much, in your case I don't believe it will matter! As you will (presumably) be dropping it after AS, it makes sense to do something you enjoy and will do well in! Maths, further maths and physics are hard enough alone and I believe RS will provide you with a refreshing break, and will also develop skills very diverse from your other choices! I wish you all the best of luck! If you ace Further Maths, Maths and Physics there will be no problem