Yeah, this is a little like what I did (I only had three hours a week in one of my subjects, however I had hours of homework from it). If you can do the five and get As in them all at AS, do it, but if not then you're wasting your time and spreading yourself too thin. Any university would go for 4 As over 3As + 2 Bs, I'm pretty sure. Only you know your limits/capabilities. (I would personally say that if you don't mind working a little harder than is perhaps necessary- or even like it - then do it, it's not too bad from my experience)