I think this is a very subjective topic as every IQR is set up differently. I can say that after riding my IQR's and my Pro 600 the Pro feels & responds in a very comparable manner to my IQR. I think the 2 sleds while similar have their intended uses. My IQR's are set up with Z-Bro's front ends, VE tunnels and EZ Rydes ETC. The areas I will ride my IQR are going to be in tight trees where I will be bumping into things. The durability/servicability of the IQR is far superior to the PRO. I have bounced my IQR off things and ridden away from them that most likely would have left my Pro wrecked.
I like the PRO and will be setting it up with new shocks, Arms etc for a better comparison to the IQR. One thing I did like in comaprison to my IQR was the vertical steering post. However the steering post needs WAY better bushings to address the steering post slop.