Andy,
I have a 2010 IQ Tour two up. The original skis were supposed to be dual runner skis. My bud who worked at the place I bought it said I needed to get rid of those as ice accumulates between the dual runners.
We installed a pair of brand new take off single runner skis and installed a set of Stud Boy 6 inch (I think, I know they are not 4") dual carbide on single host bar runners. They work pretty well.
The sled still pushes in the corners with just me if I'm moving out, , I really have to get forward to get the skis to bight in and not too heavy on the gas. I also have my front springs turned all the way up.
Innitially steering on my sled REALLY SUCKED with me and a rider. Then I learned that my sled had the stock smaller torsion springs in the skid, .405" diameter.
I ordered the bigger springs from Polaris, .421" diameter, and also installed a set of X-Click suspension blocks from Driven Products Inc. I purchesed the X-Clicks through SLP.
The X-Clicks have 4 adjustment settings instead of 3, and the highest adjustment setting is higher than the stock. I haven't had to go past the 2nd adjsutment now having the bigger torsion springs.
The bigger torsion springs also helped out the poor steering when there are two people on the sled. The back doesn't sag so much anymore therefor keeping more pressure on the skis.
Good Luck