I would take the predator!!! I ride with a gentlemen that rides a modified 400 ex and my lightly modified Predator stops all over him in torque, power and top end!!!
Take the Polaris!!!

 

I have ridden both a pred and a 400ex with just exhaust and airbox mod. The pred slaps around the 400ex but both are really fun machines to ride. Honestly though I would prefer the 400ex simply because I ride more trails and MX than drag racing and stuff like that. Just my .02

 

pred

 

I don't think you can buy a better trail quad then the pred. I do alot of drag racing and trail riding. I don't do any MX racing but Mat Nicholas does, and he has no problem wining on the Pred. Take a look at Matt Smiley he is kicking but on the Pred. Hands down the Predator!