180F or 170F Thermostat?

What thermostat are you guys using these days? These VG33E engines have always run hot, and I'm building two engines where I've drilled out the central cooling channel (right down the center of the block), and I'm hopeful this will solve issues with repetitive HG failures, but I'm wondering if anyone has an data on overall performance of the engine at 170F, rather than 180F.

I imagine the combustion process might benefit from a slightly higher temp, but unless the cooling system can keep the engine running at 180F (which rarely is the case - I see people posting temps upward of 200F at regular operation), I wonder if I should try running at 170F in addition to all my improved cooling efforts.

Thoughts?