If you hit hard enough . . .
pro tapers might fare better than any. Anyhow, I just toasted a pair of renthals when I over jumped a rhythm section last sunday. Luckily, that is the only damage. I just order a set of tag 5's from hi-per sports. They are supposedly 1 mm. thicker in the center section than renthals, and 4 bucks cheaper, so what the heck?
If you auger it in hard enough some teflon tape might save steel bars, but it won't make or break the bank on renthals, IMO. They are pretty strong, and flexible. Pro tapers seem even stronger. I bent the frame and forks on a bike once ( long story ) and cart wheeled the bike, of course, and later sold the pro tapers on e-bay ( they were still 100% straight). Basically, if you run steel bars, bring an extra bar to the track to be on the safe side. They bend fairly easy. Especially if they came on a stock bike!:D