Eric Kiptanui, recently competed twice in a day in Nairobi (6000 feet). He ran a 5k in 13:48, placing 3rd, then, a few hours later he ran a 10k in 28:17 winning it with a 2:42 last k. All of this while doing 100+ miles a week, getting ready to attack the WR in Copenhagen.. I think 58 min can be broken, i've never seen the like since the late Wanjiru.