Overlap will reduce low speed ping because of dilution but will also hurt low speed TQ so it is not the solution anymore than retarding timing would be.

Retarding the whole cam could help if you really were pushing the envelope that much, you get a later intake closing point so less low speed cylinder pressure as well as a later ex opening giving you more time to push on the piston.

I think with a stock open chamber head on that big of an engine you are not going to efficently fill the chambers at higher speed anyhow so I would shoot for 9.5 - 10.0