I don't have the x7, i have the cheap one, the z5 or something. but i love my omega. i think it shot a little better with pyrodex, but i prefer T7 loose powder. i didn't group well at all with shockey's gold crap.
so for me, with T7. i like 110 or 120gr loose powder with a 250gr shockwave bullet (or the hornady version, same bullet). i didn't get to shoot my ML last year, and don't look like i'll get to this year, so i can't remember exactly which charge worked best. with T7 powder, the equivalent of 150gr mag charge is something like 130gr. i got 2" groups at 150 yards with mine. good luck, let us know how she shoots!