Facts? Sure thing. Here are some arguing points for you.
1. Stainless steel lines were never meant for street use: They are race parts, and have a specific life span, meaning that you are supposed to routinely inspect them, and replace them after certain amount of miles. By comparison, stock rubber lines are lifetime parts, which means that they are supposed to hold up as long or longer than the life of the chassis.
2. Stiffness does not equal durability: Stock rubber lines have been bonded quite well to their fittings, and have ability to stretch and twist in the way that's not possible with stainless steel braided line. You can pretty much hang the caliper and rotor by the stock rubber line, and nothing will happen to it, it will simply stretch. The rear center line stretches quite a bit when you go full droop on rear suspension after the torque arm is installed (different movement curve than 4 link). If you try to do the same thing with the stainless steel braided line, it will snap. I've personally snapped a line on the front, while working on suspension components, by simply having a caliper slip off the hanger and fall. I've seen people snap lines at the track as well, due to age, damage due to rubbing, etc.
3. Placebo effect vs actual gain: As mentioned before, unless you get the brakes into an extreme operating temperature, enough to transfer a lot of heat into the brake lines, and make them elastic due to higher heat, you are not going to notice any actual gains. I know it's nice to think that we add parts and they make the cars better, but a lot of times that's not actually true, particularly when you use parts intended for racing use only outside of their normal use (street driving). I too have swapped to race braided lines (StopTech), and I felt absolutely no difference on the street. For people who will never see any kind of track driving at all, I would never recommend using stainless steel braided lines.
Here is video that's pretty on point about the brake lines.
[video=youtube;6LJiPDAr9f8]https://www.youtube.com/watch?v=6LJiPDAr9f8[/video]