There is nothing wrong with the standard head gasket people often go to a thicker head gasket when running high boost to lower the compression of the engine. From what I have heard 250@wheels should be fine with standard gasket with supporting mods injectors, fuel pump, ecu, turbo ect. Run no more than 10psi with the standard turbo as rule of thumb as the ceramic wheels are week. As for how much boost can I run if you are using an after market turbo it depends on what turbo you are talking about what mods you have ect.