RE: Using 2 packs of diff. Mah on one receiver?????
I've been using a 2000mA and a 1500mA on my 33% Extra for 1 year with absolutely no problems. They absolutley do not try to charge/discharge each other. I did a test on this using one battery fully charged and the other discharged to .9V/cell. The charged one put 215mA into the other one over a 1 hour period. I doubt you will ever allow your batteries to get in this predicament. Use the 2 batteries you indicated above and you will have no problems.
My only suggestion is that, that size airplane does not need that much battery, you could go with 2 batteries of 1/2 the capacity and have no problems and save weight.