Suspension fork swap for rigid: axle-to-crown confusion
Definitely you have to account for sag when measuring axle to crown distance, because that is the real geometry of the bike when it is actually being ridden. If you mention in this bike sag is 18 mm when you ride it, it should mean that your actual axle to crown distance is 459-18 = 441, thus suggesting you should use the fork corrected for 80mm travel.

Ideally you want to keep the geometry of the bike, particularly head tube angle and bottom bracket height (or pedal to ground clearance). Both are important. Head tube angle affects the steering response of the bike. Bottom bracket height defines how tall an object can be for you to roll over it without hitting it, and how much you can lean towards the side before the pedal hits the ground while pedaling (you should not put the "inner" pedal down while turning)

A bike with suspension fork actually changes it's geometry while riding due to the travel of the fork, and this is no trouble at all (for most riders), that means that a small variation in axle to crown distance would not terribly affect the bike handling characteristics.

In this case, if you chose the taller fork, you'd give your bike a slacker head tube angle, making it feel a bit less responsive on the steering, which in turn means (a little) more stability at high speed, and you would gain a few millimeters on pedal clearance. If you had the option for a third fork, shorter than the ones you already described, you'd get a bike with a steeper head tube angle, which gives a more responsive steering, the bike would feel very agile, but less stable, and you would loose a little pedal clearance.