I personally like the NGK stuff better, I think it's a little bit easier to read the timing mark. I'd use a -8 plug at that boost level.

Interooled 8psi, just start it fat around 12:1 A/F and your 20 degree mark will be plenty safe. You'll just have to sneak up on it from there, just carefully watching the plugs for detonation.

Good safe starting point though.

Trendz is spot on... buy a lot of plugs, take the time to make a pass and remove all 8 for inspection. Change the plugs, bump the timing, and try again. You can buy NGK race plugs REALLY cheap on www.rockauto.com (like $1.20 a piece)