I've been working on my own Robust Porter recipe for a few years now and it has gotten VERY close to how I like it. Although my friends (and I) thoroughly enjoy my latest version, it only scored a 32 at an AHA-sanctioned homebrewing competition when I thought it would be a little higher. I know how competitions work and that there are LOTS of influences that go into a score but, the other entry that I thought was the weakest scored a 1st place.
My point is to start off with what you think (based on your own experiences, other's recipes, and invaluable advice from everyone on this great forum) and tweak it on the next batch until you are happy with it. You will almost never get it right the first time.