Tough call
I have an 09 155 800 RMK, an 11 pro rmk 155, and a 150" camo extreme IQR 800 VES with twins, VE bumper kit, holtz front suspension, and rmk rear skid.
The IQR is by far the most fun and responsive! the pro without swaybar is right in the middle of IQR and RMK for performance, and being nimble (nimblility?) Both foctory sleds will outclimb my IQR, by just a froghair, but that is because my IQR rear skid is set up for more ski lift (much more fun for playing).
The 09 RMK feels like a tank after riding the IQR, but that being said, I just purchased an 08 rmk for a turbo project, because it is a solid reliable chassis, and I wanted to only have the turbo to mess with, not a turbo and chassis to work on.
The Pro doesn't feel heavy coming off the IQR, but just doesn't quite have the same flickability and snap. I havent done anything for clutching or changing out suspension yet. The pro needs to be laid over further and still won't carve as sharp as my IQR, but also seems less prone to blowing the tail around and spinning the sled on downhill caves, turning back uphill.
There is nothing like a new sled with a warranty, and reverse. I get tired of wrenching on sleds when there is snow on the ground, so the factory sleds are always there for me. Give it several rides to work the bugs out for a DIY sled.
An IQR can be built for quite a bit less money than a new pro, and they have the cool factor. They are also tough as nails!
My girlfriend claimed my 136" IQR with 726 motor. She can throw that around, and struggles with the 09 rmk. That being said, the 121" IQR660 with the stock 09 wide suspension is tough for her to carve in the spring.
All that being said... crap I really don't know!!! If I had Just the pro, I would really miss the IQR, and if I had just the IQR, I might miss the factory "pull rope go" and fuel injection. Keep in mind I have too many sleds and projects, leading to the factory sleds being very convenient.
I think a fuel injected motor and dragon front and rear suspension on an IQR 155 is about as good as it gets.
Everything is fun in the deep! You really can't go wrong-