Current difference between pinMode(pin, INPUT_PULLUP) and digitalWrite(pin, HIGH)? Does pin 5 or pin 6 use more power if they're just being used as a signal to an external device?
pinMode(5, INPUT_PULLUP);

pinMode(6, OUTPUT);
digitalWrite(6, HIGH);

.
EDIT:  Thanks to some links below, I hopped thru a series of threads until I found the website www.gammon.com.au/power which did tests with a 328 and found the following results with the pins disconnected (which is different than my question but seems relevant nonetheless):
In SLEEP_MODE_PWR_DOWN:

All pins as outputs, and LOW: 0.35 µA.
All pins as outputs, and HIGH: 1.86 µA.
All pins as inputs, and LOW (in other words, internal pull-ups disabled): 0.35 µA (same as before).
All pins as inputs, and HIGH (in other words, internal pull-ups enabled): 1.25 µA.
It all depends on the external device. If it has high-impedance inputs,
then it makes no difference. The Arduino itself has high-impedance on
its pins configured as INPUT. If the device draws current from this
signal, then chances are it will draw more current from an OUTOUT
HIGH than from an INPUT_PULLUP. How much more? We cannot say without
knowing the specifics of that device.
If you model the device as a simple resistor to ground (which is almost
certainly overly naive), then the current draw is
I = VCC / (R + Ro)
where R is the value of the resistor and Ro the output
resistance of the Arduino: about 25 Ω for an OUTPUT and
32 kΩ for an INPUT_PULLUP.