Think of the rubber brake line as a buffer or capacitor for pressure... it "absorbs" some of the pressure from your foot and the hydraulic fluid before it allows the full force to be exerted on the brake piston. You'll have a slight delay in SS vs rubber because of the rubber wall flex, but not much more beyond that.
I guess your maximum pressure could increase some because there are no more rubber walls to take up the "slack" in the system after you go to SS lines, but you're still able to mash your foot down on the brake pedal until it's solid with the rubber lines, right? You'll probably have slightly higher pressure if you bring your foot down to the exact same maximum pedal travel as you did with the rubber lines, but you WERE still able to "max out" your brake pedal with the rubber lines, so your max pressure wouldn't really go up that much.
I know it's kinda wordy, but hopefully you get what I'm trying to say.
The main advantage to using SS lines is to get better pedal feel and brake control.