The 400EX's cam area needs good high quality lubrication, and it is air cooled so it can run hot sometimes....going to be even more importrant with a 440!
I have run Maxima Extra ester based 100% synthetic in all my quads for years now (and Redline ester based synthetic in my trucks!), and my motors last forever and a day! Ester based synthetics are the best there is, and Maxima has a monster additive package (the best in the industry!) that will protect high pressure areas like between your transmission gears and your cam.
Run 15W50 in the hot months, and 10W40 in the cool months (or Maxima's Ultra 0W30 if you live where the winters are extremely cold). These are all very "pumpable" oils. For example, Extra 15W50 is more pumpable on a cold start than a 10W40 petroleum oil...and cold starts are where you get most of your engine wear.
Some good basic oil info:
http://forums.atvconnection.co...tid/21/threadid/520475
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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