There are many serving charts, you got that right. In my opinion, an 8" top tier will look funny, unless you have something gigantic going on top that will fill the space. If someone asked me for a cake to serve 60, I would be suggesting a 6-8-10 for 65 servings, or a 4-7-10 for 55. And yes, that's pretty close to Wilton wedding servings, but my cakes are about 5" tall with filling, and I have found sticking to one chart regardless of occasion suits my clients well. Your 8/12 is about 75 servings in my book, but the way it will look would just be wrong, but that's just me.