Get a tripod and shoot at ISO 100 (with ISO 100 film of course). Actually, for high speed film, control of the development process is very important also. If the temperature is set too high, the grains will be more prominent also. Slower film are more forgiving in this sense.
Some labs do try to shorten development time by using a higher temperature than what is recommended. Go to a reputable lab (even then a reputable lab put a scratch across my whole stretch of negative once), accidents do happen.
Press films usually has a high latitute such that useable images can still be obtained even for overexposure or underexposure by 1 to 2 stops. But don't expect the grain performance to be good because it is eventually going to the printing press where the screen printing is barely 150dpi.
I don't know if Ektapress Multispeed is still available. I find it very useful in situations where you don't know the lighting condition, or you have mixed lighting conditions.