Deal or No Deal Rincon 650 vs 400 Rancher

I hate to thank about the Palomino leaving home but a buddy of mine wants it so that being said. I ran across a nice 2005 Honda Rincon 650 that has my attention. What is the biggest difference I can expect and will the IRS make a big difference through the gullies and rocky creeks? Any thing in particular I need to know before I pull the trigger on the Rincon?

Tkx, RR