Gidday Rob and Co,
Consider this, when you use very little droop on the rear, all that actually happens is the rear inside wheel leaves the ground under braking into a corner(extreme case). This reduces grip at the rear. This has no affect on weight transfer as the car will keep transfering weight regardless of whether the wheel is on the ground or not.
The simple answer is if you want to reduce weight transfer, then change the springs/ shock oil/ roll centre at the end that requires it. These things affect weight transfer.
Heres another interesting post from a few years ago on rctech:
Actually, look at a biker doing a "stoppie" (reverse wheelie onto front wheel under front-wheel braking). There is no force from the rear tyre that is stopping it from leaving the ground, no fulcrum at the point of contact of the tyre and the road to provide a lever.
Same happens in a car, just so happens that we don't have the high/forward CG of a bike, and there isn't enough weight transfer to lift the wheels off the ground completely. What happens is they lift from the ground instantaneously, and in a 4wd car this decreases braking force, decreasing deceleration, decreasing weight transfer to the front, increasing weight retained at the rear, and putting the tyres instantaneously back on the ground, from where they will instantaneously become unloaded again if the brakes are still on!
So less droop decreases grip. Although as seaball said quite early on you need to be at very small amounts of droop (he mentioned 1.5mm, I'm inclined to agree), before you start to really see the handling effects. Anything above that and the car rarely hits the droop limiters.