I do that combination now under the current system, and am absolutely loving it. It's quite a lot of work, but manageable if you want to do it, and you have the ability. If you're getting consistent A-A* (the majority A*) then it's definitely achievable. If not, you may have to work harder, but you can still do it.
Do you know what you want to do when you leave school?
If you don't know what you want to do, I'd advising picking a wider range of subjects. If you definitely want to go into a science subject, then it's a good combination. But my only advice is you have to love science. You have to enjoy understanding more and thinking more deeply about it, because if you don't, you won't have the motivation to listen and concentrate more. So pick it if you love it, but not if you think it's just an okay combination.