As a former HS coach and College player ill tell you. 4.5 40's are good for any position in Highschool and a TRUE 4.5 is even better. I would guess the average college prospect lineman (250 + pounds) is going to run in the 4.8 -5.05) of course there will be better times and worse times than that. The average college prospect at reciever, rb, db, and lb All grouped the same cause regardless of size will be about the same will range from 4.5 to 4.6 obviously some will be faster and some will be slower. As far as Highschool kids running sub 4.5 40's (legit) i havent seen it. (coached a rb who also won GA 5a 100 m in track and he only ran a 4.52 40.
As 40 times go, in general they are considered a tool to evaluate players speed. BUT it is not always a good tool. How many times have you ever seen a lineman run 40 yards straight in a game. or for that much how often does a rb break a 40+yard run. There are many things that a college coach looks at besides 40 time. I will admit that 40 time does catch their eye, but only if its extreem. such as a 4.3 or a 5.6.
just out of curiosity, who knows what Jerry Rices' or steve largent's was?
http://pages.prodigy.net/seangates31/RiceFacts.htm