I have the exact same problem and questions! IB streams pre-calculated greeks, and I would guestimate that using those is more efficient than calculating locally for a number of strikes.

I too wanted to suggest to add 2-3 more fields for the greeks to the T8/Contract struct definition (or make it extendable by a user) and verify that IB plug-in can also populate those...Backtesting would be more efficient and RT too.