Assuming there are no issues in the system (air in the lines, etc as above) sponginess is more related to the proportions of the master cylinder to the brake calipers than anything else.
For example if you went to a master cyl that was 50% bigger your pedal would be SO hard it would be unusable.
Tell us, are you planning on racing the car or just want a better feel while driving it on the street?
Some tips:
1. Better heat capacity = Bigger rotors (not related to calipers per se)
2. Firmer pedal = Better master/caliper ratio