Can’t compare. Success on CFA will be determined almost entirely by study. Success on GMAT will be determined by acquired knowledge and natural intellect, and only marginally by preparation. GMAT samples bits of knowledge accumulated over many years. 4th to 11th grade math, grammar idioms that don’t make sense unless you encounter them in casual reading. You can study some quick and dirty rules for the GMAT, but you can’t teach your self the breadth of material.
I worked my a$$ off to pass LII & LIII. Had I not worked so hard, I would have failed miserably (much like JOE2010 on LII this year). Brains meant very little on this one.
On the GMAT, my hard work helped only somewhat. To begin my preparation, I took a sample test from Kaplan. Scored a 670 with no work. Worked my a$$ of for 2 months and scored a 690. Worked another 2 months and got a 710. 150 hrs of work to improve 40 points on a test with a 600 point range.