M20'd 520 & 525 suspension. What's the differences?

[E34-520iSE]

Just wondering what the 'official' differences are between 2ltr and 2.5 front & rear suspension. Just my car has more 2.5 parts already on it or ready to be fitted (vented discs, 525 calipers & sway bar), which makes me wonder why they made them different in the first place.

Cheers,

Shaun M