This is a hard decision.
It depends on what you like to do; PvM or PvP?
If you'd like to PvM, I would say get overloads, it makes you last longer etc.
Overload is 1 spot while Turmoil is 8 spots considered you need prayer potions or super restore potions.
Overload boosts everything to level 125 for 5 minutes.
Turmoil gives you a strength bonus of 23% + 10% of enemy's level and an attack and defence bonus of 15% and 15% of enemy's level.
That means it will make your strength, defence and attack somewhere around level ~130.
One potion has 4 doses, 6 if it's a flask.
1 overload flask makes you last ~30 minutes, while 8 prayer potions do the same AND take 7 more inventory space.
Turmoil makes your kill faster, but you can stay way much longer with overloads.
So if you're gonna PvM, get overloads first.
But in case you want to PvP, which I assume you don't since overloads don't even work in PvP.
Turmoil would be the way to go, since overloads are just useless in PvP
Here is the real question; Do I want to PvM, OR do I want to PvP.
If you know the answer on that question, you will also know the answer on the question 'Overload or Turmoil?'.
Good luck on your decision.