Are there any engine mods I can do to my wifes 550 fan to get a little more out of it?

I would imagine no one wants to touch an engine mods / 550 question due to the fact that the 550s are still not "final version" engine.

However, I think as long as you don't put a lot of "continous, steady load" type duty on the engine, it'll probably be alright.

My question, though, is to know how you define "more." Not knowing that, I imagine you'd either like a bit more torque or a bit more speed. You can affect either of those simply through doing some sprocket changes in the chaincase. Getting more overall horsepower out of these bigger fans might be iffy since they already have rather large issues - or have in the past anyway- with not being able to deal with all the heat they make.

I think the bottom end is good enough for my wife. She seems to have no trouble powering through deep snow and now that I've set her transfer blocks back a bit she never gets stuck anymore.
The top end on hard packed is sufficient as well. She's pretty light and can do 80mph on the trail if she wants. The problem is with 1/2 mile runs through the field. We live in a farming community and enjoy plowing through this field and that. My wife usually follows in the tracks left by my Crossfire but has to have the throttle pinned to the bar to do 55-60mph. Thats what I'm concerned about. Its uncomfortable for her to have to keep the throttle in that position, not to mention it seems like shes bagging the sled out all the time.
I'm pretty sure the clutching is set up for trail riding on this unit and I am wondering if there are some changes we could make there. The engine doesn't seem to ever rev very high but have no tack to really tell.
I know people have had problems with the 550 in the past and Polaris thinks they have solved it in 2007 with the sleeve changes. My feelings on this sled are sink or swim. If I mod it and it blows I'll get the 550 swapped out for a larger liquid. She loves the custom decals and suspension upgrades I've done to it so trading it in is not going to happen.
We have 1100 miles on it and besides mentioned have had no real problems except it loads up after every midrange run and back fires when shut off. So at this point I think the engine is quite sound.
Any suggestions you have are appreciated.

I would imagine there are some creative ways a person might clutch it to improve the range of performance you desire. I did a one or two tooth torque improvement in the chaincase on my 01 SS since we pull sleds most of the time. The tach on mine has never had, neither before nor after the sprocket change, had any trouble hitting top rpms though it tends to run some below that as is typical with most stock engines. These 550s do seem more "spirited" when you just putt around at slow speeds but they don't have the snap of the liquids. I don't know if that's what you like. I don't think they can do it but perhaps some clutching changes will get you close. I know Polaris did do a run of a jazzier 550 a couple or few years back. I have a neighbor, a big fellow who goes close to 300, who walks on water with his. You might look at the way some previous model 550s were set up to see if that would get you where you want to be.