Unless you want to put some money into the Fusion, stay away from it. The 600 engine is a great engine but the Fusion chassis, mostly the front end, is wacked. It's a great ride as far as suspension goes but unless your arms are as big as your legs you'll hate it. They steer like a 78 Ford pickup with no power steering. There were some problems with the 700 engine as well but off hand I can't remember exactly what they were. My buddy bought a left over 06 last year and I put 30 or 40 miles on it over the winter and it sucked! This guy also owned a 96 Ultra years back and to this day he still loves that sled.
Now the IQ, that's a damn nice sled. Another buddy bought the IQ carbed 600 last year also. Now that sled I loved. A great ride, great steering, and all around a good sled. If those are the choices you are going with and nothing else enters the picture, I'd definately go with the IQ and forget the Fusion even existed.
As far as power in the 600 compared to the Ultra you should be well satisfied unless your Ultra was piped. Stock the Ultra was pushing 105-110hp. The 600 carb is pushing 120 to 125hp. The piped Ultras were pushing upwards of 140hp though so if you were piped you're going to feel a difference.
Here's a pic of one of our rides last winter with the Fusion and the IQ. I still spanked them both with my Yammy!
