What is the best amount of DEX to have?

This was based on minimum equipment requirements (you needed at least x STR so this was the highest possible dex and still wear level-appropriate gear).

At the time it was written, the accuracy and damage formulas were not known.

Since the beginning of Global, there has never been a time when more than 40 dex was a necessity for the average warrior. Unless you want to equip special items such as the Stonetooth Sword, I'd say 40 is the max you should ever consider. 20 is possible with very little funding, 4-6 base is possible with quite a bit.

Is 40 DEX easy to accomplish with no fundings, though?