I actually sold my raptor 660 to get the yfz450 in 04. At the time it was a no brainer. I loved my 450. It IS a race machine though and was uncomfortable, no reverse, no FI, and was of course 450cc's.
Ended up getting a raptor 700 for a girl quad...LMAO. After getting it, I was alittle disappointed with my 450. I stripped all my high dollar components off and sold them away and put it up for sale. When it was for sale it was running an intake, jetting, cammod and stock can with sparky removed. We raced it against the bone showroom stock 700 and by third gear it was pullin it and just got more and more quad lengths after that. That, and while being much more comfortable and having reverse to turn around.
We soon after had two 2006 anniversary quads in the garage.
I like the 700 cause the sky is the limit on reliable mods. The 450, not so much. It gets harder and harder to eak much more power from them without costing a BUTT load of money and having a more and more unreliable build and a drag only type machine.
With the 700 we are seeing over 70hp on pump gas, and builds that will last forever and arent pushing the motors hard.
I have set my 700 up with ohlins full suspension and it handles/rides like a dream. I have moved to the 700 and have not looked back.
BUT to be honest, if I could afford it, I would own them both. Both great machines. Luckily I have my brothers to ride now an then.
The 700 IMHO is the best woods quad built and its a damn fine duner and might end up as popular as the banshee for the dunes.
The yfz is an awesome track machine, and is fun in the woods and dunes, but again in my opinion not near the machine the 700 is in those two locations.