The armour should be of equal consideration to the slide protection. Ever grazed your leg running by something? Lets say for arguments sake at around 15km/h. Usually, any pants of some thickness will go a long way in protecting you. Try running directly into a knee-high wall at the same speed and there's a good chance you'll break something.
Now, quadruple the speed and you're still moving slowly in bike terms and consider the possible differences and defenses. You better have some serious impact protection for the street as there are obstacles everywhere! No sliding off the track into sand or across grass into a tyre wall. Consider something with D3O, CE2 or equivalent protectors in the hips, shin-knees and possibly tailbone and thighs.
For the sliding, Kevlar is good but degrades significantly when exposed to moisture or UV(Sweat? How do you dry it?). The manufacturers don't like to talk about or test that ;-) Nylon,cordura etc melts at high temperatures whether that be touching a hot exhaust or sliding down the road. Leather works well here but also has a tendency to come apart if not of good quality or thickness. And all of these worthy materials are NOTHING without great stitching to hold it all together!
I used to distribute 'the "previous" strongest jeans in the world' and can attest to their slide protection. But they also change shape, stitching frays and the waist trim/securing is a joke. Not to mention they are a 1 hit wonder with the cotton shell buffing clean off in a good slide.
Search: Bull-it jeans if jeans are your thing.
Please consider that at the end of the day, you only get what you pay for and you ought to pay for how much protection you want, right? Want to be safe driving down the street buy a hummer. Want to be real safe? buy a tank. Want to be safe and fast? Go talk to Bruce Wayne.
For me, it took a while, but I've finally landed my mangled bag o bones in a Streetguard3 2 piece I scored for less than 1/2 price by smart/lucky shopping and love it. I think it is a Wayne enterprises product
