fz4vgq, GPI is almost identical between the two when you adjust for the slight spine difference (a .487 spine at 10gpi vs. a .500 spine at 9.7).
Spine is a slight difference. The Beman's follow standard 340, 400 and 500 spine, but the CX 90s are 530, the 150s are 487, and the 250s are 373.
If you are caught between spines this could be important. I shoot CX 150s, but may be jumping to Beman 400s for my next set with a slightly heavier/faster bow.
I also like that the brass HIT inserts come standard with the MFX b/c I have to buy the brass ones for the CXs.
I've been shooting CX 150s for several months and they are very durable. I've missed the target several times, hit all kinds of things, and slapped arrows plenty, and the only arrow out of commission is one that I couldn't find.