Mike- Cable routing is an aspect that I have given a lot of thought, mostly motivated by solving routing problems on factory made bikes, during servicings at the shop. I also run my rear brake on the left side lever because my right hand is better at modulating lever pull, the front brake is the one that will either kill or save me dependent on how I use it. I strongly like casing loops that are as gracefully curved around the corners of a bike. Especially at the head tube where a cable/casing in a really short length/tight curve can add steering forces. Being a short guy the lever to frame distance is less then most. On my calipered road bikes I have the forward cable stop placed on the right side of the TT about four fingers width from the HT. It is placed around the TT at about the 4 or 5 o'clock point. The rearward stop is on the TT's left side to allow the casing loop to the caliper to be minimally curved, again about 4 fingers from the ST. The cable runs under the TT (and on some frames I place my HPX pump under the TT too, if you do this take care with stop placement and pump location) and through a plastic liner sleeve. On the Canti bikes the front stop is the same and the rear one gets placed on the right side and how far from the ST is determined by the casing loop to the stay stop (or brake arm if a linear one).

Here's a shot of my S&S bike with the cable crossing under the TT as example. Note that the stops are further from the ST or HT then usual. See how smooth and few bends the casing loops have? I do get some paint rub off in a few spots. This has never been an issue for me, sort of like are getting winkled skin where we stress it. But it would be easy to add casing guide loops right on the side of the HT or lug edge to contain the casing's rub to a, perhaps, SS loop made from a spoke. There are lower head lugs with this feature out there but I'd make my own loops. Andy (who has sworn at bike designers many times, may they be required to work on the bikes they design over and over )