I've just purchased a set of new 4703 STIs - I only wanted the front left but it worked out the better option to buy a boxed pair, from reading up apparently they work better than the older 6700/5700 10 speed shifters so thought I'd give them a bash. I'll be using the triple on the Sabbath September with a 5800 as I want to use my mid cage 11sp RD and stick to an 11-28 cassette (a 24/28 gives me 23" low so will get me up at least a 14% gradient so covers most bases). The right will probably get used at some juncture.
I've however managed to order the wrong size clamp FD to match the Tiagra
further reading has revealed one of Mr.Shimano's techie employees (at Eurobike) stated that the pull ratio is the same on the triple 4703 as it is for the former 5703/6703 (the 4700 right is compatible with no other RD apparently
)
If anyone wants one in the less common size larger band size, this ebay shop has them for about £17 posted.
FD-5703 34.9mm