I've gone through the Cadet medical, and for me it came after Stage 3 interview. So I'd have to agree you should find out as much as you can about being medically ok for CX before going thru all the hoops.
Why do CX leave it so late for the med? By the time you do the medical they've interviewed you 3 times, watched you do 2 team exercises and about 8 hours of tests. Obviously the medicals take time and money but since the rqmts are essential would make sense to me to do it between the 1st and 2nd stages. Its quite possible for Cathay to waste a lot of time on an applicant who can never be a pilot.
anyway, back to the thread, good luck to you mate, if you can pass the D15 colour test and you're running 5 miles a day you are probably more medically fit than most pilots!