Time Trial / Time Trialling / TT

MDCC, here's a question, what sort of fixed GI should I go for on a 10 mile flat TT? I was thinking around 80-85, but I have zero experience of riding fast fixed.

I just rode one tonight on 93" and did a 24:21, which is an average cadence of ~90rpm. YMMV, I know people who ride roughly the same speed as me on gears of up to 120"