It depends what you mean by "direct".

Some derivatives use different number of clocks per cycle (and Dallas is one of them) than the original Intel 8051, so comparison by clock speed alone is not enough.

For example, AT89S8252 max 24MHz, 12 clock/cycle

T89C51RD2 20Mhz, but 6 clock per cycle, so effective 40MHz when compared to 8252

And notice the captial H's andy