A lighter spring will enguage the clutch earlier while the motor is making less power & cause a smother takoff & some times will bog the motor too much if poorly tuned.A heavier or stiffer spring can be identified by thicker wire hence the descriptions of .09=soft,1.0=medium,1.1=stiff & will enguage later at higher rpms when the motor is making more power & can be called violent at times causing loss of traction but will also slip more if you use a slow finger instead of whacking the throttle open.Look at someones clutch bell that uses 1.1 springs & you can usually see signs of extreame heat,the bell will have a blue & redish color on the outside & the car will rocket out of corners if traction is available.Composite shoes are usually lighter than alum & enguage later/higher rpm if using the same spring tention as an aluminum shoe & usually slip more than alum shoes causing A more friendly take off even though the motor is making more power when they hit.Some people like the 2 aluminum & 1 carbon combo but look at the inside of a used clutchbell & se how smooth it isthey usually have groves worn in them & aluminum built up on them.Now how well do you think that soft plastic/carbon shoe will hold up grinding against those groves & buildup? stick with all one or the other & you can use 1 softer spring to help get the car rolling with that one early enguaging shoe slipping some then wait for the other 2 shoes to come in a little later with heavier/stiffer springs.
Or go to a slider type clutch & have infinite adjustability.Werks & firioni both make those style.