What do you mean "inaccurate?" I described exactly what you linked to, except I used terms that allowed it to be extrapolated for all bigcubes puzzles. Saying "make a 1x3x4" doesn't really apply when you are solving a 7x7.
The major difference between megaminx and 3x3 is that all turns on the megaminx yield even permutations. Besides that, the calculation is very similar to that of 3x3.
I've had 2 ll skips on 3x3 in about 3 months. I'm pretty sure I haven't solved 2 million cubes in that time. Yayz! Plus one of the ll skips I was timing, and I had super easy f2l.