it does not work without a line of code between the digitalWrite´s, looks like then there is no change at all on the line.
reading back from the LCD costs a Pin more, and also time, when running pure in assembler and having enough I/O left ok, but for the arduino i think that speed is ok...
check my thread in the exhibition http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1240088162
ive postet a vid there to show the speed. think thats enough speed 