Thicker oil will change valving in basic terms, and more oil will increase bottoming resistance. I guess I could see that working, my problem is on my dirtbikes I already need the stiffest springs available because I am a big guy. I went with a stiffer spring rate because I need it just to hold it up in the stroke and then even stiffer than usual for the compensation of what the snowbike does to the front of the bike. My springs are so stiff they coil bind before the seal would slam and I had to grind the guides to get that size wire to fit inside the tubes. Then I played with the shim stacks until I got something I like and I am very happy with it.
No way I could ride these forks in the dirt, after I first put the springs in I wasn't sure about what I had done, they felt crazy stiff...In the snow I love them, even on trail they feel great to me. It seems counter intuitive but a stiffer spring rate will often make a smoother more compliant ride. On a stock dirtbike I squash the thing. I need really tall risers, use ATV bars, lower the pegs sometimes by a bit to try and fit the bike to my frame. At times I have had spring rates that I thought would be pretty close and the bike rode harsh (I love rocks) when I have increased the spring rate the feel of the bike in the garage is harsh but the feel when ridden was smoother than the softer spring. Starting further up in the stroke makes a difference and the only way to do that is spring rate...or air which does the same thing basically.
I have zero experience with the airpro, I do have a few hot rods on air ride and a Funco Sandrail on bags. The air springs do strange things because the spring rate isn't consistent. as the spring compresses the rate rises, this goes for all air suspensions. It's like a basketball and it takes air specific valving to control a rising rate spring...probably not a big deal in the snow but it has been on the dirtbikes as evidence by all the MX teams chucking them in favor of a traditional spring fork. The Air is great as the rising rate offers a ton of bottoming resistance like increased oil and I am sure the MX teams will continue to work with an air fork because if they can make it work it would be substantially less un-sprung weight and weight in general, but the rising rate is tough to control. I am by no means the suspension master, I love the rising rate spring on the Funco, the set up works cool in the dunes, but even Funco when they built a race car a few years ago went to a coilover instead of the air spring. On my hot rods I actually prefer the ride of a traditional spring but the ability to lay the frame on the ground and look cool trumps the ride in that case.
All that said in the snow I'd just find a way to deal with the snowbike quirks at the price you feel like paying and go with it.
