Regarding the Betta stocks, I heard that some patch changed the payout cap from the 80 or so it was to about 50. Can't verify that but it's as good an explanation as any.
I can verify it's not true.
I was having problems with Betta not rising above 50ish, as i described on the last page i think.
I ended up loading a save previous to the Hotel Assassination mission, and decided to make as much cash as i could before running that to optimize my 50ish percent, since that seemed to be the max i'd get. So i went and did the Kifflom stuff, and maybe i didn't pay attention to what i read before, but i ended up not stealing the car (with 2mill, i guess), and delivering it instead.
Whether that has anything to do with it or not, i don't know, but when i ran out of things to do, i bought Betta stocks with all money on all characters, did Hotel Assassination, and watched Betta stocks rise this time up to 81.xx% (and stabilize at that return percentage for almost an ingame week).
Now Michael has about 2.5 mill. I kept the savegame from before the Kifflom missions, in case going the current path doesn't land me enough money to buy all properties in the end, but i'm thinking/hoping it will, considering many say they got to billions without running the Epsilon Program stuff.