Texan, I'm in the Austin area & if you'd like, I can get you info on the GAF products.
If it's Class IV impact AND wind resistance you're after, have you considered going metal (realizing that your neighborhood may not allow this).
What kind of price differences are you seeing in the different products? For IR (Impact Resistance) ratings, hou HAVE to use a specific hip & ridge cap shingle; make sure your contractor isn't skipping this (i.e. ask to see a parts list & compare it to what is on the ship list from the parts supplier). CertainTeed's IR hip & ridge caps are more expensive than GAF & I have no experience with Malarkey (I think they only recently started penetrating the Texas market).
Additionally, take a look @ what kind of warranty you are getting from your contractor. I highly reccomend that if you go with GAF, you get someone who can install with the Golden Pledge (100% parts coverage for 20 years, not 'just' field & hip / ridge).