hmm...just some quick updates on those looking to upgrade.
Double brake master Pump - you can get this from the e34 wagons or e32's. boosts the brake pressure. very effective to improve pedal feel. but might be too strong if u're using steel braided hoses, limited modulation allowed before full pressure. but def worth the money vs performance. very easy to get the ABS to kick in, especially in the wet.
e38 brembo 4 pot calipers n disc n oem pads - have to be modified to fit the e34/e36/e46 etc. coupled with the double brake pump, it allows more modulation of the pedal compared to the stock 525i's. stopping power, just got the car today, so not much use yet. tried a few times, seems to stop the car a little bit faster than before, but might be psychological. let me run in the discs and pads and i'll update later.