If I may ask, where did you get the crank set? I heard Shimano is now offering crank arms down to 160mm. I'm more of a grinder than a spinner and I think 160 is about ideal for me.

Second, you may be obsessing, but I don't think you're wrong. 50 up front and 12 in back doesn't give you much top end. Of course, you really shouldn't even need it unless you're on a descent anyway, but when you are, it's always nice to be able to keep putting power into the crank.

One of my bikes I tried 150mm arms. That crank set came with a 50t big ring and it has a 11t on the rear. I run out of crank pretty quick on any noticeable descent.