It is hard to find good, unbiased fact based oil information. Two good articles...no marketing hype, BS, or bias:
http://www.sportrider.com/tech/146_0308_oil/
http://www.sportrider.com/tech/146_0310_oil/
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Southern California Deserts and Mountains....
Desert: 450R, 400EX
Technical Trail: Rancher 420 and 350 4X4's
Kids: Two 250EX's and TRX90
Dual-Sport Bikes: KLX250S and XT225
Past rides: 300EX, 2wd Rancher 350, Recon, TRX90, Z400, LT160, LT80, Warrior, Blaster, CRF230F