i run the galfer superbike lines on my 600. very awesome. chances are you wouldnt notice the difference between kevlar or stainless.
but yea, anything is better than stock. in my opinion, doing the rear is useless, but to each his own. i could see Armenian's point with using it for stunting, but if you are riding hard on the street or track, the front is probably all youll need. probably the best thing you can do for your braking system if you had to choose one thing to do.
i have the brembo master cylinder, vesrah pads, and the superbike lines.. my bike stops better fucking well.