I'm thinking of upgrading to the 8350 as well. I plan to overclock as much as is stable on air. Why sabertooth over the m5a99fx? Just because it has two extra power phases? Browsing through forum posts, I've found a lot of unhappy campers with the sabertooth and almost none with the m5a99fx, but maybe that's just because the sabertooth has been around longer.
I have the rev 1 board , never had a problem , putting an 8350 ib it now , ran with an oced 1090 for 1 1/2 years , board has great features , lots of temp sensors , runs cool and 5 year warranty and easy to assemble (wires from case have little adapter to plug wires onto then snap it into header on board ) . Not sure what problems people have had but my experience is it's a great board ,lots of OC potential
Don't have a m5199fx so can't comment . Other board I have that is good is gigabyte 890-fx ud5 .