I'm not busting brush in all the time in (equally humid) East Tennessee, but over all I've been pleased with the eVent gaiters that Ron Bell at MLD made me. Other than having to replace the shock cord periodically, they've held up to a lot of trail miles. Again, I was wanting something mainly to keep out trail debris--they won't be nearly as robust as the OR, etc. but I'd venture they'd be as cool as anything you'll find on the market.
http://mountainlaureldesigns.com/product/superlight-gaiter/