Tell us about "11:1". Is this a measured and KNOWN 11:1" Is this a "my brother's friend's hooker girlfriend said it's 11:1"? If you don't know 100% FIRST HAND then we might need some compression test numbers. ....and it wouldn't hurt anyway. I would say an "HONEST" 11:1 engine would use a plug one, maybe two heat ranges colder than stock.
All I know is I had a couple sheets of paper that came with the sale (from the owner) with a long list of mods and specs. I guess I'll just go with a "stock" plug for now and see what happens. Thanks.