After rereading the OP I'm still going with my first impulse: do both. I'm a great believer in the pedagogical (pedagogical?) value of bikes, they can teach us. With the combination you will have the opportunity to learn much more. Just as a minor example, you can compare the two+ on the same route and get a much more nuanced understanding of what you want with respect to climbing, descending, cornering, hammering, breezing, etc. Of course the risk is that then you will start to think about what you want in the next bike...