So my bike has Shimano Tiagra ST-4600/4603 brifters (it's a triple) but is fitted with long-drop BR-R451 calipers. In theory, these should be incompatible because of the change in cable pull ratio, which Shimano seem to call "New Super SLR" that happened in the 4500->4600 / 5600->5700 etc. transition.
However, I have found conflicting sources as to whether this is OK, including the Shimano compatibility chart at hosted at Celebrazio which firmly says "No!" (although if you're using the flat-bar lever it's OK?); whereas the Shimano Line-Up chart seems to think it's all right to use as an alternative to the short-reach in-series caliper. Also, a previous edition of the compatibility chart says that mixing the older brakes with newer levers is permissible.
I presume this is the same situation as using the short-reach brakes from a previous series of the groupset with the newer levers, in which case is there any solid advice about making the setup work?