Without diving into my Sim's you shouldnt be gemming pure mastery, are you talking about hybrid gems in red sockets?
Generally Mastery scales our heals less than Int would, in terms of HPS/HPM--- int, of course, also scales Echo of Light given that the base heal will be bigger. (so your echo is a % of a larger heal).
Unless you want to run a full simcraft, take a look at
http://www.healadinne.com/HealCalc/healcalc.html and look at the individual 1000 point rating changes, for the spells you are interested in after importing your own character.