I have St. Augustine grass as well. I push mow 22,000sq.ft. of lawn every 3 or 4 days during the growing season. Great fucking exercise and I love it. I mow at the highest setting my mower will go which is 4 inches. I mow slow (I take my time) and never, never cut wet grass. I can't stand mowing wet grass. I never do that shit. My shit looks like thick green lush carpet. I use Milorganite at a rate of 15lbs./1000 sq.ft. four times a year. Yeah that's a lot but it is what my lawn calls for. I also mulch mow which is very beneficial for your lawn.
Here is the mower I use (the grasscatcher is useless to me):
This is a great mulch mower with two cutting blades
Honda HRR216PKA
http://powerequipment.honda.com/lawn-mowers/models/hrr216pka
I have purchased four sets of blades which get me through the cutting season. I go through all four sets and sharpen them all and tune up the mower in the offseason.
Also, I only use Non-Ethanol gasoline in my mower and anything I run period.
Here is the mower I use (the grasscatcher is useless to me):
This is a great mulch mower with two cutting blades
Honda HRR216PKA
http://powerequipment.honda.com/lawn-mowers/models/hrr216pka

I have purchased four sets of blades which get me through the cutting season. I go through all four sets and sharpen them all and tune up the mower in the offseason.
Also, I only use Non-Ethanol gasoline in my mower and anything I run period.