I've got the Joe Rocket Phoenix mesh pants to go with my Joe Rocket Phoenix mesh jacket. I thought it would be helpful to have that zipper connection that ST_Jim mentioned, but I have never ever actually used it. Had some issues figuring out how to get in and out of the gear when zipped together, though in truth I didn't try very hard to work out how it's done.
After the crotch zipper failed for the second time in the three seasons I've had them (maybe not entirely a design flaw; the pants may no longer be the right size) I switched brands to Sixth Gear.
As far as heat deflection / coolness goes, it's pretty much a wash between them. Both brands are quite tolerable (for me at least) in hot humid mid-Atlantic summers such as we both experience. Both brands have full-length zippers up the outsides, I assume for extra ventilation but certainly to make donning and doffing easier; I never ride with them unzipped (seems like it partially defeats the purpose-- if I open the zipper I've exposed skin to possible abrasion in a slide...).
I typically wear bicycle shorts or nylon convertible cargo pant shorts beneath the riding gear on hot days, and on really hot days a micro-mesh CoolMax tee shirt. (Tip: cotton shirts are about the worst possible choice in hot or cold conditions. They absorb moisture; in heat that moisture turns the shirt into a wearable sauna. In cold it turns it into an ice machine. Get some purpose-made outdoor upper wear, made with a moisture-wicking fabric, to dramatically increase your comfort.)
Heat management aside, I like the Sixth Gear better because I prefer its closure system and the removable liner (useful for cooler weather), but I like the pocket design on the Joe Rocket better and thought they were slightly easier to get on and off than the Sixth Gear. And, I'd be in agreement with other posts on this thread that Joe Rocket build quality is not as good as other brands-- but it's half or less the price, too.
Finally, as others have also noted: heat management and dissipation is a whole-body strategy and it starts with your head and neck. Anything and everything you can do to shed heat from those areas will make your entire corpus more comfortable. Not easy to cool your head while inside the helmet, I know, and I don't have a lot to suggest except a wicking do-rag. A wicking neck gaiter, kept wet, will not only cool your neck it keeps the sun off the back of it preventing skin damage and also heating.
Next work on cooling your torso. I've no experience with cooling vests so can't speak to their effectiveness. But wicking fabrics for your shirt will help. And if you get them wet, the evaporation does help a great deal though in high-humidity conditions you don't get so much of that.
Good luck, and stay cool!
