One more consideration to consider when purchasing an older GII/IIB. Where it is registered (country) and how does the maintenance and aircraft requirements differ between where it's been and where it's going( new country).
If it's coming from abroad where there are no, say CVR/FDR requirements, then plan on paying anywhere from $300,000-400,000 USD to get it up to code, so to speak. There are a plethora of other gotcha's like RVSM, TAWS etc..
Get a good person knowledgeable in the field.
Personally, and this is just my opinion, a late model hush kitted GIII would be better than a C 600. Forget about the GII.