Have a look at the Garmin site. The Automotive section (GPSs for cars) provides a comparison tool. All you do is tick the models you want compared and they will appear side by side with the differences highlighted. It's fairly useful and should give you enough information to make a decision.
I know you posted this 4 months ago, but if you have not yet made a purchase , here's a little buying advice. I buy most of my business "stuff" (paper, ink, envelopes, etc) at Staples. Since I am a "member" I get weekly emails from them showing sales for the upcoming week. I bought my Garmin Nuvi 265WT Aug. 2010 & at that time Staples was selling it for $209.00. HOWEVER, they were offering it at a 30% discout & an "instant 10% savings" in the store. $130 for a $209 GPS worked for me
Then in Feb 2011 it was on sale at Staples for $99.00 All these GPS's have a manufacturer's warranty & I'd hesitate buying it from Walmart, but check out other stores online (Costco may have them real cheap too). Good luck, but now that it's April you probably already bought one