I've done the following mods to my Stampede:
-Air release hole filled
-'Servulus' spring (10+kg load)
For indoor wars, I use the stock spring (no need for epic ranges).
Lite/Heavy silis: 14-15m
Heavy silis: 30m or so
I highly recommend the Serv springs, which can be purchased off Oznerf from 'Servulus'.