For the application questions, talk to an admissions consultant. That's really not my area of expertise - I'd just be speculating. I've heard that some candidates with non-quant backgrounds can take some math classes to show proficiency (you have to earn A's!) - calc, stats, that kind of thing. But, again, talk to someone who actually knows: an admissions consultant. I'd recommend MBA Mission.
First, congratulations! I know you want a higher score, but great job increasing your score again. The average improvement from official test 1 to official test 2 is 30 points and the average improvement from official 2 to official 3 is 0 points. So you've beaten the average - well done!
Next, it isn't a problem at all to take some time off - the schools won't even notice. They really do just use your highest score; that's all they care about.
The schools will only see whatever scores you submit to them, so if you don't submit GMAT scores, they won't know you took the GMAT.
I do get a decent number of questions about switching to the GRE. When you're this far into one test, it's usually better to keep going with that test - just take a break (as you want to do!) when you get burned out.
The quant can be a bit easier on the GRE (depending on your strengths and weaknesses*) but the verbal isn't easier, just different. Your vocab has to be pretty strong to do well on the GRE verbal.
*For example, geometry is tested much more on the GRE than the GMAT. If that's a weakness for you, then the GRE might not be easier.
But here's the most important thing: some schools state that they prefer the GMAT and Haas is one of them.
http://mba.haas.berkeley.edu/admissions ... ments.html
So, if you want to apply to Haas, that's a pretty strong reason to stick with the GMAT. (And Tuck used to say that they prefer the GMAT, although they took that off their site sometime last year. So maybe they've changed their mind.)