It is difficult to compare a 500 to a 650 cc machine. The 650 is going to have more power, every time. Also check the weights. Artic Cats run heavy, sapping power from their engines. If you are looking at 500 cc, then you should check out the Suzuki Vinson. It is rated as having better power to the ground than the AC, even though they have the same engine. For some reason the Vinson's configuration gets more power to the ground than the AC. Likely, it's because it's lighter than the AC. Check out www.atvtv.com for a good review of the 500 class machines. They do a fair job of listing the goods and bads of the different quads. As for solid axle versus IRS, it's a matter of preference. I'm not sure how much it really makes a difference. I would be more concerned about overall handling of the machine.