I'm using the avid hs1 rotors with saint m810 brakes and so far it's all working out good. I haven't noticed any loss in power versus my friends saints with ice tech rotors.
if your rotors are in good nick u probly dont need to replace them but juicys are getting on these days so if they are worn out rotors then your are def losing some potential. in saying that u dont need to replace them with shimano ones but fresh rotors of good quality would help. the ice tech rotors do work really well with the saints (i run them). if ur rotors are getting thin due to use then u are losing some of their heat sink capability so they will get hotter than give u brake fade