Here is a little rant on the early CR big bores of the 1980s:
The CR450 was made 1 year, 1981 and it is a TERRIBLE bike. The gearing is horribly spaced from what I understand.
I have not riden one and I have not mapped out the gear pattern however, this is the word on the street.
The CR480, by all accounts, is the better bike to get which was made in 1982 (4 Speed) and 1983 (5 Speed). The 1983 is the better of the two years, but both bikes are supposed to be quite good.
The 1984 CR500 has a detination problem, but it can be fixed by reshaping the dome of the head, costs about $100, Harry Klumm can do it.