I guess that "someone" would be me
I wouldn't worry in the slightest about skimming the head reducing compression ratio. The g40 has the combustion chamber in the pistons with a pretty much flat head so skimming the head makes such a small difference to compression ratio you needn't worry about it, as I said on clubpolo.
The metal gasket is from a mk4 polo 8v engine and will raise compression if you want it to be higher.