You can bypass the Arduino method and access each of the 8-bit ports by name, e.g. PORTD gets all 8 pins of port D, which happen to correspond to arduino pins 0-7. There are no nibble or word operations, although since we're talking about an 8 bit microcontroller one could argue that the 8 bit operations are word operations.
it seems that one line of code beats four any day...
Not if 4 lines are easier to write correctly or understand as compared to one line. I was taught once upon a time that above all the code should be correct and easy to understand. Worry about performance later, if you find there is a performance problem.
-j