Completely depends on what you are going to do with the quad. If you are going to be trail riding or racing desert or woods (basically GNCC) the XC SOHC engine is the better way to go because it has more low-end power. For motocross where a mid-to-top-end engine is preferred with lots of overrev, the SX DOHC is the better way to go.
$7700 OTD is a hell of a deal by the way. I'd jump at that. It makes my SX price seem not worth it ... kinda
Sponsored by Dirt Fiend Racing (DFR) of Mesa, AZ ~
2004 Honda TRX400EX (RED)
PEP, Hydrodynamics, Lonestar Racing, Rath Racing, Pro Armor, Pro Taper, ASV, Streamline
2009 KTM 450SX ATV (ORANGE)
Fox Racing Shox, Lonestar Racing, Precision, Houser, Motoworks, Hiper, Fuel Customs