to do with the way i drive the car, i find the ds2500's to be a nice pad on the front, for road they stop you well and provide a nice feel, the mu's on the rear as they lock up the wheels piece of piss, and under hard braking they balance the car better for me, if i was to run really aggressive pads on the front, it makes the nose dip too much and then on turn in will give me unpredictable oversteer, with a aggressive pad on the rear and a slightly easier pad on front when i brake hard the car stays more level...
gives slightly more slip on the front than the rear
as i said in the rx7 im removing the abs, so im going to run some oem pads front and rear whilst im running the engine in and to get used to the difference in braking, then will stick the mu's on rear and either the ds2500's front or possibly the dixcel pads front as i have heard good things about them...
this settup is just my personal preference being rwd will prob be different than you in your fwd settup, i think you are going in the right direction with the mu's though, they were designed for drifting which means they need bite and no fade... they work well on track im sure you will be happy!!