As a general rule of thumb, 4 cores sharing the L3 is better in gaming than 6 cores sharing the L3.
Your motherboard selection will likely hold back your OC'ing quite a bit, but will actually make a great low-cost performance platform.
For best gaming performance you should run those four Thuban cores with the IMC/NB at 2400-2500MHz from stock 2000MHz. Your NB VID might well do it at stock, but 1.2-1.25v is no issue here. For each 10% you increase the IMC/NB speed, memory bandwidth is increased 3-4% and latency is reduced 3-4%. That's good.
As far as the CPU and the overall gaming potential, I vote:
1) 19x200MHz at 1.388v, no Turbo;
1a) 18x200MHz at 1.388v, with Turbo; and
3) unlocked, with or without Turbo.
I haven't tried it yet (not really a big gamer) but with Option 1a the Turbo function adds a +2x to your cpu multiplier across 2 cores (each core with a volt bump). In some games this may provide a boost.
If your motherboard can handle the volt delivery. I'd take what 1.388v will give you.