If you do a search you will find quite a bit of discussion on cross-drilled brake rotors. Some claim it is simply a visual and a non-performance item while others see their benefits. I have them on our 300E and have appreciated their qualities. New Mercedes are coming with them standard now.
I would consider installing front ones only. You do not need to change anything but the rotor. There are cross-drilled, slotted and a combination.
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