I have to say first that I am very biased when it comes to the 670, and all of the RV motors Ski Doo use to produce. Certainly the big tripple is going to be faster overall....but when you factor in all the other considerations the 670 is the way to go. The are very quick, full of torque, and a twin (so less headaches). It's amazing that this motor is still giving 700's and 800"s a true run for their money even today.
Alot of guys have to have the latest and greatest and in my opinion waste a lot of serious cash. Having a nice 670 with a good suspension upgrade is truely the way to go: less cost, far more reliability, a sled that will hold it's own with the newer iron, great looks, and at the end of the day more cash in your pocket. Newer does not always mean better, and in my opinion the 670 is the way to go.