THE 600 is the best bang for the buck. You will get tired of the 400 in a month. Not enough power.
The 500 is a great all around machine, but for a few bucks more....you got the 600.

 

price difference between 500 and the 600 in my area is $470.

for that difference i'll take the 600!

 

I had a 500HO, gf had a 400 and I now have a 700. Wish I had stayed with the 500. Ya the 700 has a bit more power, but not real noticeable to me, top end is about same maybe 3 mph differance. The 700 sucks gas bigtime. As for the EBS, I wish I did not have it, riding slow it wants to come on and the ride is jerky. Would sure like to get rid of it. As for the 400 I found it rather weak when going from the 500 including top end, acceleration, and pulling. I use mine for trail riding, pulling trailers, plowing (60"), and pulling logs. Would definately reccomend the winch. As for not being able to test ride the machines, I feel if I am spending 6K I am going to try it out. The dealers around here encourage it. May want to try calling around to one that is more receptive to the potential customer. Good Luck.