Again, new shields and lines are inexpensive and make everything look great. The bending of shields I believe is for the rear brakes when swapped to R32/S3 setups.
If the OEM brake upgrade can cope with up to 280BHP, 4 piston calipers can go higher but ultimately the efficiency varies with the disc and pad choices that accompany them? Using solid, cheaper discs (the term cheaper is relative here) will probably mean less stopping power than the 2 piece discs which are expensive (both relatively and actually!).