I’m not sure I agree with some of the stuff on that thread re. Shimano cable pulls
I run the SL-R770 10spd flat bar shifters on my roadie. These have the same cable pull as std road STI and I’ve run them with 6600, 6700, 7800 and even MTB mechs perfectly, which suggests that they all have the same cable pull.
AFAIK the latest 10spd MTB kit is different though, so if you run the SL-R770 shifters (or any 10spd Shimano road STI for that matter) then you can’t use a 10spd MTB cassette (or at least it’s not ideal…). You need a road 10spd cassette (Shimano or SRAM).
In short, if you want to run flat bar shifters on 10spd then either
– buy the SL-R770 shifters and keep everything else 10spd road kit, or
– but some 10spd SLX shifters, cassette and mech