I just heard this in a Pershing series Lecture from National WW1 Museum at around 10:40 as well as 12:40. The lecturer specifically mentions Battle of Megiddo at 12:40 and how it was the fastest till the advance of XVIII Airborne Corps in Desert Storm. How true is this? Did WW2 tanks not beat this? Battle of France? North Africa? Or even Six Day War?
There may well be some fine print in this. What's an 'advance'? Is it a movement of the front line? Is it a raid? A recon penetration? But my short answer is that he is wrong on the face of it.
Looking up a map, it seems that the front line in 1918 moved at most 50 miles in the first 30 hours, which is a pretty good clip. However, since I've been reading up on Japanese armored doctrine (which was much more advanced than people tend to give it credit for) recently, immediately checked my notes to compare with the operation to seize Chengde in 1933 by a completely motorised force (Including a company of tanks) under Major General Tadashi Kawahara. It did 320km (about 200 miles) in three days, and succeeded. It was only a regiment in size, but if you divide distance by hours, I think you get a better rate of speed.
That's not to denigrate the Megiddo advance, mind. It took two days for 7th Panzer to do the 60-mile run to Rouen in 1940. On the other hand, the run by 7th to Cherbourg was almost a hundred miles in a day, though I'm offhand not sure if there was any opposition.
As another counterpoint, when VII Corps moved North after Dragoon, it took a week to go from St. Tropez to Grenoble, also about 200 miles. This was considered a very quick advance, although in fairness, the terrain was hardly flat.
A week is also what it took 56th Panzer of Army Group North to do the run from Memel to Daugavpils in the opening of Barbarossa. 260 miles was the distance run in eight days by 24th Panzer to Bobruisk, also a slower rate of advance than Megiddo, if one looks at averages. However, who is to say there wasn't a 130 mile advance in a day, then a three-day fight, then a slower advance after that? I've not looked into the details.
Your six-day-war guess may be correct as well. Abu Ageila (Near the Israeli border) to Abu Zenima (Gulf of Suez) took less than two days (7-8 June), and seems to be about 140 miles. And that wasn't done in a straight line, they went via Ras Sedr.
Presumably there is some criterion that LTC Steed was using to come up with his conclusion, but absent details as to what those criteria might be, I would put a very large asterisk next to it.