Interesting -- I got the cool wings last summer and found them extremely helpful. The first day I wore them, I soaked them in cold water at a water fountain, and they dried very quickly.
http://www.teamestrogen.com/prodDE_CW.html
I like the jacket style because I can wear them with tank tops.
I generally ride one day per week after work, which means riding in heat and humidity during the summer months. I find the location of the sun in the sky makes a huge difference -- it might still be pretty hot and humid at 7 pm, but the lack of strong sunlight makes it okay. Whereas I tend to have serious problems during the afternoon when the sun is highest.
I've also done my share of summer rides in late afternoon, starting at 4 pm or so. It's definitely better than riding between 1-3 pm but can still be pretty hot. I would make sure to have some kind of electrolyte replacement for a 2 hour ride at that time of day.
Also you're right about watching what you eat earlier in the day. Try to avoid heavy/high fat meals, because they take longer to digest so they can weigh you down while you're riding even if it's hours later. You might need to play around a bit with the timing of what you eat during the afternoon so you don't bonk during the ride.