Just sold my 02 Grizzly 660 and bought 04 1/2 SP600. After first weekend on SP here are my opinions:

1. Engine - Grizzly wins by slight margin. It felt a little stronger and sounded better with its louder
grumbling noise. Griz topped out in low 60's, haven't tested SP's top end yet. Throttle response seems
similar on both.
2. Suspension & handling - Toss-up. The Griz may have rode slightly plusher but the SP is real close and
its steering is noticably lighter. Other suspension and handling characteristics seem similar. The SP
suspension components (and also driveline) make alot more noise than the Griz. I don't like that. The
SP is roughly 140 lbs. heavier than the Griz but to be honest I don't feel it in its handling.
3. Ergonomics - Toss-up. I seem to sit slightly higher on the SP but I like the placement of the instruments
better than the Griz. Trans shifters are on oposite sides on these machines. I have no preference
regarding that. I like the single lever brake on the SP.
4. Transmission - SP600 wins. The trans on both machines are similar in most respects but the shifter
stalk on the SP is clearly superior. It's much easier to use (the forward-low to reverse pattern on SP is
awesome). The Griz's shifter is notchy, hard to engage, forward to reverse is a pain in ***, and the
zig-zag pattern sucks.
5. 4 wheel drive system - SP600 wins. For my kind of riding, this "leave it on and forget it" system is
superior. I got real tired of constantly pushing buttons, sliding levers and pushing more buttons on the
Griz. It's too complicated and the lag between limited slip and full lock 4wd is a problem. Backing up in
full lock 4wd is a joke on the Griz (although new models have over-ride button). The SP is either 2wd or
full lock 4wd (no limited slip 4wd). This suits me fine and its automatic application lets me concentrate
on the trail.
6. Brakes - SP600 wins. For some reason the brakes on my Griz (even after replacing) were always
mushy. The SP's seem OK and I prefer the one lever.
7. Misc. - Toss-up. Racks on SP600 win by slight margin. SP's are very easy to remove for cleaning and
won't chip like the Griz's but they are harder to hook bungee cords to because of the thickness.
Floorboards are better on SP. Griz has more storage space under seat. Access to engine/fluids is
similar. The Griz in my opinion is better looking with its mean front end. The red suspention components
on the SP are cool looking, however. The tires seem similar (apparently they cheapened the tires on
the 04 1/2 SP's).

CONCLUTION - Both machines are similar in many ways but based on the above the SP wins primarily because of its 4wd system and to a lesser extent it's trans shifter. There is one crutial thing not mentioned above. THE GRIZ IS NO GOOD IN WATER/MUD!!!!! Steam from the engine gets into the carbs and it sputters and cuts-out. This was a huge problem with mine and many other Griz owners. Yamaha has supposedly fixed the problem with vented side panels but I still hear about it. There are other issues with the older Griz 660's that they claim to have straightened out. This remains to be seen. I know there have been problems with early SP twins as well but the Griz's inability to run in water/mud is huge.

I've run Yamaha's my entire life. I didn't want to switch brands but felt I had no other choice. I considered an 04 Grizzly but after the problems I had with the 02 (there were others in addition to the sputtering in water) I decided to try Polaris.

 

I think the Polaris 4wd only works in forward, don't you have to keep the button pushed in when backing up? Also see what that POL(or is it POS) is like when it's a year old.