According to dinan it is increased.
Dinan's Stage 1 Suspension System provides greater control over body roll by virtue of carefully calibrated spring rates designed to work in conjunction with the original-equipment standard or EDC shocks and struts. Dinan lowers the M3 by 1/2"" front and rear for improved suspension geometry and an even more aggressive stance. Matching bump stops and replacement front guide supports are included that actually increase suspension travel by 7mm (on top of the 3 mm already added to EDC equipped cars) for improved handling capabilities along with surprisingly civilized ride quality. The higher spring rates, increased suspension travel and improved suspension geometry give the M3 even more grip for faster and more predictable cornering capabilities. All of the EDC system features are maintained for cars equipped with the option.
mods: akra evo, dinan 3.45 diff, ess akra tune, dinan stg.3, Alcon bbk, HRE P40