3/4 solid hardwood over gyp-crete?

[C7RVETTE]

do i need to screw down 5/8 or 3/4 ply over the gyp-crete? The gyp-crete is about 1/4 to 1/2 inch thick. The gyp-crete is laid over a

3/4 inch OSB sub floor.

thanks for any help.