Ill just add to this, if you have a mythstone on the gear say hp+25% then you cannot roll hp% of amy kind an that gear until you use garent to remove the mythstone. Similarly for exp gain, cooldown reduction, clear cast..
but ive never tested WD+50% because it actually appears to be different to the regular epic affix..
if i have a weapon of base 2500 damage, endow for +50%, epic WD+100% and epic WD+5000 then it would be 2500+(2500*0.5)+(2500*1)+5000 which totals 11'250
Not compaired to contrary belief of 2500*1.5*2+5000 which would be 12'500.. theres a small difference