The Brit tanks and even the French FT's at least had a decent chance of crossing shelled terrain. Those Schneiders and IIRC there was a big French one just did not due to superstructure overhanging the treads.

6 pdr is right about 57mm.

There were quite a few armored cars from then, some were not too bad as long as they didn't hit rough or soft ground. Or too much hill. Or.....

Oh, and from post-war military books the really big important factor on the use of tanks is using them in large groups. The Brits pulled it off once of twice but only enough to demonstrate the principle. That's why I rate the terrain crossing ability so highly, and the mechanical reliability. It's also a surprise to find out how many Panzers did not make it to the start areas in the Battle of France, broke down on the 250 mile drive.

The book I had (never lend your references!) went so far as to list the ones that didn't make it to the start area and how far the ones that did got, account by account. Circa 1930, the book is "The Fighting Tanks" IIRC and has a reccomendation from then-Major Patton.