Yes, possibly. There are some devices out there that run with a 230nS E pulse too.

Beware of the controllers with different numbers of cycles per machine cycle (Dallas, Siemens etc) they'll cause grief too.

Generally speaking a vanilla MCS51 device operating with a vanilla 44780 controller type on a VCC of 4.5~5.5 and memory mapped is safe below 8Mhz (I used 7.3728 'cos its easier to divide for the serial port :) )

regards,
dm v2.5.1