I've ridden in 95-100+ temps and learned a couple of things. Riding with a Camelbak for longish rides will keep me better hydrated. I add Elite to the water to help keep my electrolytes in check. I also carry a couple of bottles on the bike to be used as shower bottles and I douse my jersey and head with the water to help keep me cooler. Also, wearing a cycling cap helps keep sweat out of the eyes, the head cooler, and the visor really does help block the sun and makes it seem a little cooler.
If you do plan to ride in the hottest part of the day, you may notice your speed is down, particularly if it's humid. Plan accordingly for this--you don't want to plan a long ride, putter out, and then experience a heat stroke. (People who have experienced heat stroke do not tolerate certain temps.)
Add about 5 degrees from the heat coming up from the road. You might want to adjust your tire inflation to account for this.
Sunscreen seems to keep me cooler as does jerseys with sleeves. I thought I'd be cooler in a sleeveless jersey but found it to be the opposite.
When your heart rate is climbing and you can no longer get cool, it's best to get off the bike and call it a day. The sun will fatigue you more than you realize and you might be surprised just how inviting that nap is. Enjoy your ride and keep your phone handy in case you want to call a friend to meet you for ice cream. :)
