Still the issue vexes me.
I went here:
http://www.geistware.com/rcmodeling/cg_super_calc.htm and banged in all the measured values for the Magnum, and selected 15% static margin. So guess what - it tells me 198mm!
Maybe one day I'll start moving my CG back from 140mm until I can't fly it anymore. Then I can build another one and move it ahead a little from there...
MJD