I'm running a water/meth kit on my FST, same setup you guys would use. No tuning is required if you use properly sized jets and correct water/meth mix.
I run 60% water and 40% meth. I have a 2gph nozzle after the intercooler and a 1 gph nozzle spraying into the turbo compressor (raises compressor efficiency and reduces lag). This setup has worked flawlessly for me.
If you use water meth with the stock turbo you will make more power. Ecu see's low IAT and less knock, therefore it keeps timing at peak performance levels instead of derating. Also something to keep in mind is that on a turbo mountain sled your intercooler is always plugged with snow and even if its not you aren't going fast enough in the mountains for good air flow. So WOT runs in deep snow you will get very high intake air temps without water meth.
To take it a step further, spraying into the compressor will increase your compressor efficiency thus acting like a larger compressor. Turbo stays cooler, less lag, higher efficiency.