Well for the time it's still "easy" to get the GCAA ATP through the FAA one. Should you consider a JAA standard training today I would recommend to get it in Europe instead of a speculative frozen GCAA one. In the mean time going for a quick FAA ATP then GCAA conversion when needed will not cost that much and will give you the unfrozen license...
In my opinion, as a part of the CPL-IR it is quite more educative to experience some real weather, icing and other "classic" procedures (NDB, restricted airports etc...) instead of being vectored for ILS approaches on 3500 m long runways in clear sky, no wind, no rain, no terrain etc...