If you are referring to a character display, the extra 4 bits won't give you much performance boost. The display starts up in 4-bit mode. It uses 4 wires to communicate. If you let it use 8 wires, it may sound like it will communicate faster, but I've heard experts here say there's no apparent improvement in speed. You can think of the 4 bit as 4 pipes and 8 bit as 8 pipes. You can transfer water with one pipe if you want.