Almighty ring and Legendary potential?

4% per line.
Rule of Thumb:
1st tier increases by 1% per rarity increase
2nd tier increases by 2% per rarity increase
3rd tier increases by 3% per rarity increase.

Interestingly enough this is wrong. Level 0-30 equips go 1% (rare+), 2% (epic+), 3% (unique+), 6% (legendary+) for single stats, 1% (epic+), 2% (unique+), 3% (legendary+) for all-stats.
So what you'll see in practice is 6%-one stat or 3%-all stat on the primary line, and 2%-all stat or 3%-one stat on the secondary lines.
The best Legendary Almighty Ring is thus 6%-6%-6%, while the best you'll ever actually see is 6%-3%-3%.

So I suppose the question is, 6%-12% primary stat vs. 5 atk 7-all stats. Or possibly vs. 10 atk from DABRs?