For those sort of temperatures you should look into cooling vests. Being in Seattle I have not felt the need to invest in one (but wish I had over the past month) so I will leave it to others to comment. You can also get cooling thingies that go around your neck. I might be getting one of them before next summer rolls around. Regarding jackets a mesh jacket is probably your best choice. You will be sacrificing some protection for comfort but overheating is dangerous in itself. If you have the money, I love my RevIT Turbine jacket. It has CE Level 2 armor in the shoulders and elbows but you have to buy a separate back protector. Just remember you will need gloves, boots and hopefully pants as well (and obviously a helmet).