Okay, I've taken the plunge and have now had installed Shimano 77700 Dura-Ace bar-end shifters, Shimano BL-R400 brake levers and Shimano CX50 cantilever brakes, with the original all-in-one pads replaced by Ultegra brakes shoes (with a swivel back, allowing toe-in) holding Swisstop Flash Pro BXP pads.
So, first impressions - the new brake setup is phenomenal, very powerful braking, but with good modulation, leagues ahead of my previous setup (with Tektro 720s). I really wasn't expecting such a dramatic change to be honest. BTW this is with the stock fixed saddle wire that came with the CX50s. The R400 levers are fine and probably contribute to the good braking. Not as comfortable to ride on the hoods as my old Campag Veloce levers, but not too bad and I only ride on the hoods in heavy traffic anyway, usually a bit further back. The levers do exhibit a rattle, pretty sure from the plastic inserts - will either remove these or wedge them in with thick grease or something.
The bar-end shifters have worked out fine so far, the indexed shifting on the back is precise and the friction shifting of the front triple is easy to do. Takes a little bit of getting used to, moving my hands down to shift, but am finding it okay so far.
Will try to post some photos of the setup at the weekend.