One thing that puzzles me is your use of Open Pros and 700x23 tyres on a King of Mercia, you seem to be putting road tyres on a touring bike. Nothing really wrong with that, but with your audax style of riding why not get the Mercian Audax Special frame
You also mention some medical issues, given that it, might be good to make your bike a bit more comfortable so I'd recommend putting 700 x28 or 32s on the King of Mercia and spend money on some really nice hubs and rims. I like White Industries Racer X hubs and Velocity Dyad rims for credit card and loaded touring.