They only synergize off base skill points not + skills. If you did the calculations of + skills you could get 40k+ Fire Balls and 25k Hammers.

Depending on your sorc scenerio, it would be a good idea to go into Energy Shield and Tlekenesis if your for PvP. If your a baaling/MF Sorc then put into your armor. Putting a few points into Cold would be very useless sincei t takes like 6 skills to get to Frozen Orb and even at the high lvl of like 45 Frozen orb only does about 1,300 damage iwth its synergy and if you have no high Cold Mastery it wont do fucking shit vs Baal games. Why waste your skill points when your in a party and there will always be something dealing with cold in a baal run.