Similar ratio for Intellect?
I would use 2-3 verse per primary stat. It can definitely change between class/spec based on each ability and how it scales with AP/SP.
If you want to napkin math it, you can do it easily by yourself. First, remove your neck and look at the tooltips of your important spells. Write them down. Next, equip a BoA neck that has the CORRECT primary stat (4 int in this case) and NO verse. Again, look at the tooltips and write them down. Finally, equip a BoA neck that has the WRONG primary stat and VERSE (so the 4agi/5verse neck). Again, look at tooltips and write them down.
Look at the differences between the INT necklace and no necklace. The amount it increases is what 4 int gives you. Then look at the differences between the VERSE necklace and no necklace. The amount it increases is what 5 verse gives you. Each spell can have its own primary stat ratio, so each spell may be different. You'll have 2 equations for each spell, so solve the most important damage ability, or solve all of them and look at the range of ratios.
But basically you'll get something like 4int = 20 more damage and 5 verse = 10 more damage (these number are made up). So 1 int is worth 5 damage, and 1 verse is worth 2 damage. Which means 1 int is worth 2.5 verse.
Its not super accurate. It changes per class/spec and even spell, and it doesn't include elemental force - but its a solid rough idea.
Like vers, agil also applies benefit of defense for rogues. Agility adds to your dodge rating. For whatever stupid fucking reason blizzard decided to hide that, it's still a factor that helps your rogues in melee combat.
But imo vers is better if you can get it to a higher ratio. A mix of both is great, too.
Helps to get Deja Stats for these kinds of things.
+1 for Dejacharstats addon. Every twink who cares about gear should get it.
I don't know that agility adds any appreciable amount of dodge anymore. I remember talking about it near the beginning of the expansion, but I can't remember if it doesn't add it anymore, or if its just absurdly low.