Rip, a 2004 Polaris Predator 500, is the sporting/race ATV I decided on buying for myself, since I had done so much offroad riding and competition when I was young. I needed something to do during the fall, winter and spring months in Ontario where a motorcycle isn't ideal and racing cars is out of the picture. Sticking with my complete motorheadedness, I bought Rip. Yes, I made up that word. 
It's fast, fun, handles like a dream and has loads of suspension travel. It's more comfortable than the "pure" race quads like the YFZ 450 or TRX 450 while being easy to insure unlike my first choice, the Raptor 660. Not that it's any slower! Insurance companies suck... initially I was going to buy a Kawasaki V-Force 700 since it would be easy for anyone to ride - though just a bit powerful for beginners.
I'm happy I ended up with the Predator 500, though - fast enough for anything, handles great and has enough comfort to ride on the trails all day. One of its exclusive, and nicest, features is its Pro System steering geometery that eliminates bump steer.
Specifications
Known Stock Performance
The Predator will do about 75mph stock with a good surface to do it on, and can accelerate through the gears with the best of what is available in 2004. It's a real ripper of a machine.
Articles & Reviews
ATV Connection, Jan. 2003 - link - Predator vs. Glamis 440
ATVing.com, 2003 - link
Sportquad.com, 2003 - link
ATV Connection, 2003 - link
Quadpit, Fall 2003 - link
ATV Rider, Dec. 2003 - link
Off-Road, August 2002 - link
ATV News, Jan. 2004 - link - vs. KFX 700, Raptor, DS 650
ATV Illustrated, Dec. 2003 - link
ATV Illustrated, Dec. 2003 - link - Predator vs. YFZ 450
Modifications!
I wasn't really sure that I was ever going to modify my quad, but it turns out that I ran into some used parts from a guy that was going to the "next stage" with his machine (580cc big bore) and he offered to help me not only install the parts but also tune the machine properly for them. And he did... what a huge difference the mods have made to my ATV - more low end power, much more midrange power, and a top end rush that lifts the wheels clear of the ground in 3rd gear sometimes just with power.
167.5 main jet, needle clipped one richer
70 pilot jet
Idle jet turned 4 turns out
Slide spring clipped 4 coils
Pure Polaris pipe with 12 plates
38 tooth rear sprocket
Ground shifter to clear frame and moved down one tooth
Superbike airbox mods