Biknut: check this out:
Interlube International, Manufacturers of premium Opti oils, Opti-2 and Opti-4
Opti 2 might not be a synthetic, but it actually STARTS working the best at high temperatures as it actually reforms the texture of the metal to reduce friction. It's pretty amazing stuff, and *ALL* of the local mower shops I've been to in my area use it in all their 2 stroke equipment and swear by it. I live in West Michigan. Meaning I have about 6 months of decent weather and about 7 months of tolerable riding conditions. I have used Opti-2 on all of my builds save my first, and have *never* had a problem with it in any weather condition.