When should you Cap your str?

You can cap it at less than 104 if you plan your build ahead and save yourself restats. Look at what equips you're likely to have every 10 levels and how much str you would need for them.

For instance, at 80 I had TT80 gloves, 69 mold pants and TT80 necklace which gave me 18 str so I could put less into str. At 90, I plan to get Sky demon's pearl and lunar glade cloak so that would get me 14-15 str so again I could put less into str. Once you add enough str to wear all your equips, then add 5 dex per level.

104 for end game LA + end game daggers. More than that only if u want to wear helmet...Or u can try to get a nirvana helmet that requires only 104 of str but they just add half HP comparing with normal helmets...