Just got my custom Gunnar Sport done - with custom 210's... I'm 6'8" with a 38" inseam. Given the info you've provided, 180's might suit you. Nice thing is those are out there by major mfgs. I have a Cannondale sporting Dura Ace 180's, for example.

My impression us far is that the cranks definitely feel different and I feel like I have better power/torque application. More of my leg feels like it's part of the conversation now.

Keep in mind that opinions vary on the long crank topic. It made sense to me, so I went for it. We raised the BB up on the frame geometry, but also kept it more or less sport touring-longer chainstays etc.

Let me know if you have any questions. The KHS Flite 747 seems like a cool way to get in the game if the rest of the frame fits and 105 fits the bill...

LAX