What is the farthest someone can travel in 8 hours?
Outside the box? Almost 1,000 miles, if they're falling the entire time. Terminal velocity for a human (and, therefore, a humanoid PC) is about 120 mph. Absent travel to the Plane of Air or subterranean bridges guarded by Balrogs, it's unlikely you'll find a way to fall such a distance, of course.
Otherwise, your answers are essentially identical to those on the other question since wind walk is only 6th level and it's virtually impossible to reach a sustained move speed of 300 otherwise, so the answer is 240 miles unless your DM rules effects can modify the speed granted by the spell. All you need to do is look at the answers on that question and eliminate the movement from bonus actions, Dash actions, effects which last less than an hour, etc.
Magical movement forms can be increased by fast pace according to the DMG p242, so you can fast pace travel with this spell to gain +33% distance for a total of 320 miles.
Ignoring wind walk:
Wood Elf: 35
Monk 6: +15
Barbarian 5: +10
borrowed Transmuter's Stone: +10
Mobile feat: +10
Longstrider from potion, wand, etc.: +10
That's a move of 90, so 72 miles.
However, that's the same movement as a Riding Horse with Horseshoes of Speed (60 + 30). A Druid 5 could add longstrider to that to get to move 100, or 10 miles in an hour. If 8 such mounts are available, such a character could ride all 8 hours at a fast pace, which allows you to cover double the distance, or 20 miles an hour. That's 160 miles.
Realistically, the phantom steed spell is probably the most practical method of travel. It's a ritual, and creates a mount with speed 100 for 1 hour that can travel at a fast pace of 13 miles (it's not made clear why it's 13 miles and not 20). That's 91 miles, assuming you spend spell slots three times and use 55 minutes to cast the ritual version 5 times. Or, if your DM rules you can cast the ritual from horseback, that would be 104 miles. Potentially more if your DM rules the steed can be a target of longstrider (+10) or benefit from Horseshoes of Speed (+30).
Interestingly, it's actually difficult to say what the movement here does if our monk/barbarian above drops the Transmuter's stone and the longstrider effect or just climbs onto a riding horse. The rule of thumb given (1 mph per ever 10 feet of movement) is the special travel pace, and the +33% movement bonus is the fast special travel pace. The PHB says, "Certain special mounts, such as a pegasus or griffon, or special vehicles, such as a carpet of flying, allow you
to travel more swiftly. [See the special pace rules in the DMG.]" The DMG then says:
The rules on travel pace in the Player's Handbook assume that a group of travelers adopts a pace that, over time, is unaffected by the individual members' walking speeds. The difference between walking speeds can be significant during combat, but during an overland journey, the difference vanishes as travelers pause to catch their breath, the faster ones wait for the slower ones, and one traveler's quickness is matched by another traveler's endurance.
A character bestride a phantom steed, soaring through the air on a carpet of flying, or riding a sailboat or a steam-powered gnomish contraption doesn't travel at a normal rate, since the magic, engine, or wind doesn't tire the way a creature does and the air doesn't contain the types of obstructions found on land. When a creature is traveling with a flying speed or with a speed granted by magic, an engine, or a natural force (such as wind or a water current), translate that speed into travel rates using [10' movement = 1 mph, fast pace is 133%, slow pace is 66%, et al].
It's possible that this rule is meant to include anything that travels at a rate other than 30, but it's certainly not that clear. It actually sounds like the game assumes you will travel at a rate of 30 regardless of what you do unless you have some means of magically enhancing travel. You could have a party or Wood Elves outfitted with riding horses, and they'd move just as fast as a party of Halflings in full plate. In the real world, when travelling long distance by horse it's common to either move at a walking pace or alternate riding and walking to spare the animal, so perhaps this is what is intended. Still, it's strange that just casting longstrider on your horse changes you from 3-4 mph (6 mph for 1 hour) to 7-10 mph simply because you get to employ special travel pace rules.