Having a reference to work from is half the battle. If you like the contact points on your existing bikes and you aren't having any issues like knee pain or something else that would indicate a problem, you have the information you need to start talking to builders. How long have you been riding? If you have the experience to know that your fit is right for you, you don't need an outside opinion.
You'll be thrilled with a custom steel bike. Getting a bike fit for you versus picking a small, medium or large will be time and money well spent. Pick a good builder a throw some trust their way.