@BelArg
I believe the OP is referring to an A330-300 sim, not a B747-300
UK CAA BCARs was a 7kt adverse Xwind requirement.
And 1:1 ratio between Xwind and Vmcg increase isn't a bad rule of thumb.
But, to be honest, the Vmcg test is such a test pilot "party trick" - no "average pilot reaction time" involved there - that I doubt ANY line pilot will keep his aircraft on the tarmac if he gets the critical case. Remember, the TP/crew are BRIEFED for the test - yet when we do calculations involving pilot reaction times for "normal failures" we use anywhere between 1 and 3 seconds. Vmcg is SO sensitive to pilot reaction that realistic reaction times make the values obtained for cert pretty much a theoretical number, nothing more or less.