a good motor shop should be able to shave as little as 2.5 thousandth of an inch from your head. AFAIK, too high a CR, or piston to valve clearance becomes an issue before the head being too thin is a problem.
You can get off the shelf "head saver shims" to compensate for when the ehad as been skimmed too much. AA gaskets (In Aussie) can supply them. aj130s08 = 0.8mm thick and aj130s15 = 1.5mm thick.
get it skimmed, and them measure your combustion chamber volume, and calculate your compression ratio. As long as you can get decent fuel, (98 octane) 10:1 should be okay for the street, depending on your tune.