1. You can fit a 30" tire on the S models with no other modifications, maybe just a little preload adjustment, that would give you an increase in ride height. Also, Brute Performance makes a bracket lift for the S model that can gain you a little more height without adjusting the shocks at all.
2. You are never going to be able to keep up with the 1000cc sport machines in many situations, particularly in the sand or high speed trails, but a popular upgrade for the Teryx is an ECU reflash. You remove the ECU from your machine and send it in to be reflashed, this will raise the speed and rev limiters on the top end as well as in diff lock. They will also remap fuel and timing tables to give you a more well rounded power curve and a little more HP. Popular options are VForce John and Alba Racing. I used Alba racing and I had the ECU completed and back in my hands in less than a week. You may also consider a clutch upgrade if you are looking for something specific like low end torque, VForce John would also be a great resource for that, just give him a call and I'm sure he would be able to give you some options.
3. Wheel spacers are a very popular upgrade to these machines as well and there are many options available, check out Dune Gear and Super ATV for quality choices. Aftermarket rims with different offsets can also gain you width without needing to run spacers.
