A buddy of mine has an '06 M6 (albeit a badly thrashed example) and it runs very well. 2 pulls when cold, and runs all day without a hiccup. A tad on the rich side (both gas and oil) but should last a good long time. John's sled has 350 hours on it and is still on the original top end. The sled is very easy to carve with (read: very little effort) so it would probably be something your wife gets comfortable with in short time. I hear that the 2009 steering posts (adjustable for height) will fit the 05 and up models.....Might not be a bad investment. That way the wife can be comfortable on the trail, then raise the bars for added leverage in the POW.
Might look for a Boss seat too......Limited storage on this sled, and the wife might be more comfy with a taller seat.
If you're buying used, look for a clean low hour (don't go by mileage- the nub for the speedo breaks and folks don't replace it until they sell it......John's sled shows a little over 600 miles but 350 hours.....hmmmmmm). Must've been ridden reeeeeaaal slow, huh??
Check A-arms and bulk-heads for bent items and worn bushings.
Happy hunting.