REG:
Average score = 63%
Trending score = 75%
Finished 58% of the questions, but got through about 80% of the q's the first time I took REG.
Actual score = 84
The first time I took REG I got weaker in all tax areas and stronger in the business law section. For the second (and final!) try I didn't spend much time on bus law at all; just focused on tax and ethics. Still reviewed bus law and had the basic concepts down though. Got stronger on all the tax/ethics areas and weaker on bus law... but it worked!
So my advice for those retaking: spend 90% of your time on tax. Especially since SIMS are almost always tax related