Interesting thread so far, especially the contributions from zzyzx_xyzzy.
One thing I haven't seen discussed so far is the fact that the coefficient of friction of a soft material (like rubber) on a hard surface is pressure dependent - as the pressure increases the coefficient of friction decreases.
This is because the usual assumption that true contact area is proportional to normal force breaks down if one material is soft enough to elastically stretch around the asperities of the other. A good practical illustration of this is race car tyres - the width and low pressure (just over 1 bar) give the highest grip possible.
In theory, therefore, lower front tyre pressure will give you better braking. Does the theory hold up in practice? I've not done the experiments but I'll give it a go tomorrow.