Why do the stainless work better?
Are the stock lines not rigid enough, and bulge?
I believe you target precisely the mechanism, steferf!
Rubber (or other flexible material) brake lines are elastic; brake fluid is incompressible in its liquid state. Steel braid surrounding brake lines direct the pressure from the master cylinder piston to the caliper piston(s) more efficiently. The brake lever motion goes almost exclusively to clamping the pads against the rotor, rather than diverting the force to expanding flexible brake lines.
Make sense? Didn't think so, not a problem.
Not sure whether I'd choose braided brake lines over an oversized rotor, if I could have only one (put both on at the same time on my bike).
I doubt either or both affect measurable stopping distances, a function of the tire tread and the riding surface, but as mentioned, the brake response time appears definitely lowered (braided lines), and the rider modulation capability (oversized rotor) is improved. Result: More controlability, and safer riding potential, IMHO.
EBC oversized rotor and teflon steel-braided, plastic-coated brake line shown on '07; example only, Gen 1 (not Gen 2) acknowledged.
Braided Stainless Steel Brake Lines
Braided stainless steel casing protected by clear vinyl covering for durability.
PTFE 62 inner casing for minimum expansion under pressure.
Provides stronger, more progressive action than stock.