Are you using the SPI pins for anything? If you use the SCLK pin as your WR line, you can get a hardware clock from it at half the crystal frequency by doing a dummy SPI transfer.
First of all, an LCD has it's own internal processing time. No matter how fast you pulse the enable pin, the LCD can only work as fast as it's able.Secondly, the physical response time of an LCD screen is slow (in the millisecond range). What benefit do you get from accessing it faster?Lastly, if you know your clock speed, you can make a delay circuit of about 1/2 the period of the clock then XOR the two together and get a 2X clock.It all seems pointless though (unless I'm missing something).
//Pseudo codewr low;nop;nop;nop;nop;nop;wr high;
//Pseudo codewr low;nop;nop;nop;wr high;
pin1 low:pin2 high;pin2 low;pin1 high;
I'm not up to date with the mega, however, if the SPI is in the double row header then for now it is used as I have an LCD shield.