Hey Bison,
As a high school football coach and college strength and conditioning coach, I can assure you that 4.4's are possible in high school. I had a kid a few years back that ran down Drew Astorino ( the safety from Penn St.) in high school like he was standing still. Drew ran a 4.5 his senior year at the Nike camp. I also know another local kid who is out of this world, in most everything. He was 18 years old, 5'8", 175lbs, runs a 4.46 40yrd dash, benchs 400 lbs, squats over 500, and set 3 Junior Olympic weightlifting records in Kansas City at the age of 15.
Real world times for the fastest of the fast are somewhere in the 4.1-4.2 range. Mike Wallace the WR from the Pittsburgh Steelers, ran a 4.19 in a indoor facility. Thats the fastest time of anyone in the NFL. Ive seen several athletes who are quicker, but not faster, in events like the shuttle and turn and dash. Sprinting is all about the start, not so much speed. Most still top out in the 20-21 mph range, they just dont have the good start like some others. That is why we judge 40, 100, shuttle, and just flat out closing speed and average them out.
I had a 6'1, 210lb fullback in high school 3 years ago that was only a 4.6 timed guy, but when he broke into the open, say "bye"...he was gone. His flat out stride was incredible and he was so strong, no one could drag him down. He gave up football to be a doctor.
Thanks
Coach