if you have not reached a plateau, there is no reason to increase the dose.
however, 750 before 1000 would be a step up.
you have to increase arimidex depending on the conversion to estrogen.
did you have bloodwork?
in theory yes, the higher the testosterone, the higher the estro, the higher the dose of arimidex to take ... but I repeat: it is very subjective.
finally do not forget that if you want to gain more, you must absolutely also increase the kcal and the intensity of the workout.
testosterone alone won't do wonders.