" So I suppose this is kind of important and seen a lot of people wondering which gems to use
It all depends on your spell power and how valuable crit is to you.
What you want to work out is the % increase from a single point of intel and the % increase from a single point of pvp power (1/265)
Seeing as pvp power gems give double you need it to be worth at least double intel because of the crit gained from intel (which can't be calculated in because of preferences, caps, spells etc blabla)
So 1 intel as a percentage increase of spellpower would be 105/spellpower by default, 111/spellpower with intel or 116/spellpower if you include kings/monkshit/motw.
When that number is lower than the % from each point of pvp power then the DIRECT increase from intel is not as much as PvP power.
You obviously don't need to reach that level because you get double from gems. So the point you are looking for is when the int sp % increase is is less than double that of pvp power (1/530).
So unbuffed you are looking at: 105*265/2 = 13913 spell power
Intel: 111*265/2 = 14708 spell power
Intel and kings/motw/monkcrap = 116*265/2 = 15370 spell power
Above these values the direct increase from Intel is less than that of PvP Power.
Again: This EXCLUDES the crit from intel.
Now... Set bonuses. Lets say there is a set bonus of 50 intel: You are now comparing 130 intel to 160 pvp power and so the intercept changes.
160/(80+50) = 1.230769
For example, unbuffed: 105*265/1.230769 = 22608 spell power
So somewhere above 22608 spell power that set bonus is no longer viable and that point depends on how much you value the crit from that 130 intel.
Keep in mind that the % increase of spell power increases the damage of your spells based on the specific calculations and therefore does not include constants.
These constants are different on every spell so if you want to work out the increase on a specific spell, use that.
SUPA IMPORTANT: Having a higher spell power coefficient in a spell does not make spell power any more viable than PvP power because you are comparing percentage increases.
TLDR;
This all depends on how valuable crit is to you as well as the constant damage value of the spell you are casting.
Unbuffed: PvP Power gems are better than int gems somewhere over 13913 spell power
Intel: PvP Power gems are better than int gems somewhere over 14708 spell power
Intel + kings/wtfever: PvP Power gems are better than int gems somewhere over 15370 spell power
"
SOURCE ARENAJUNKIES
i hope it helps