I think the standard is 1mm. Speaking from no experience lol, but 1.2 or 1.4 would be as high as i would go. I remember speaking to a guy who said you can run 1.4bar on standard internals if you use a 1.4mm gasket.
if you get a JAM fuel cut defender it removes fuel cut and HKS fuel cut defender moves fuel cut, so is slightly safer, however it makes the car run leaner throughout the rev range.