Originally Posted by
linus
I can confirm that Deore 9sp RD works with 5700 10speed STI lever.
Also, you can use Shimano MTB front derailleur with STI lever.
It may work, but I'm guessing it's not the buttery-shifting of the matched group-set. STI shifters are rather finely made, tightly spec'd, and optimized to work in conjunction with their matching derailleurs. If you're adamant about STI I'd stick with matching levers and derailleurs,
especially for a new build.