Arreat Summit is the original D2 info site from Blizz and has some info.
Weapon Speeds vs Classes
Certain weapons are more effective in certain character classes’ hands. The listed speed ('slow,‘very fast,’ etc.) is relative to other weapons for that specific character. Weapon Speed descriptions, as well as their actual swing rate, can change for a weapon when wielded by two different character classes. The listed speeds ('slow, ‘very fast,’ etc.) further describe a range of speeds; a ‘fast’ dagger might be slightly slower than a ‘fast’ mace, but both will be faster than a ‘normal’ club.
When numbers are listed for Weapon Speeds such as [0], [-20], [20], the higher the number is, the slower the Weapon Speed. So, [20] is the slowest of the three Weapon Speeds.
If I have a ‘very fast’ sword, and I equip a magic item that Increases Attack Speed, will it be even faster?
The answer to this is yes as well, however at some point the speed maxes out, and they cease to get faster.
Is there any way to tell when you have reached your maximum Weapon Speed?
No, there is no easy way to tell when you reach the limit. You can get faster than “very fast”. (Try the Barbarian Frenzy skill to see just how fast you can get.) It would be very hard to reach the limit, you can almost always get faster. All weapon types probably peak at the same speed, so the fastest possible Polearm weapon swing would probably be just as fast as the fastest possible one-hand sword swing.
I personally use https://diablo2.diablowiki.net/ for most of my item information. However, for the more nitty gritty info the site you listed is much more robust.