Jet fuel is my business, so I will throw in some things to think about that makes this calculation stuff a little more difficult to figure out.
are both international routes, and depending on the circumstances, aircraft may have access to bonded/un-bonded fuel. Bonded being not subject to full taxation depending on several factors related to the acquisition of the fuel, and un-bonded being regularly taxes per federal/state/county rules.
Of course, the larger commercial type aircraft will also receive special ITP rates from the fuel supplier that are very low margin given the high volume involved.
The G650, however, probably will not incur low rates, but still cheaper than retail depending on whatever contract fuel provider they use (if any) or volume taken.
All this, in addition to the other stipulations you mentioned above, make a calculation difficult.
For what it matters, NY Harbor today was wholesaling jet fuel for something like 3.20/g (dont know exactly)...my guess is that it was being sold to domestic carriers for somewhere around $3.90/g, but thats pure speculation on my part.
Edit: I should mention that the fuel is not (usually) sold directly to the airline, but to the fuel provider at the airport who then of course does some math on their part for the work involved and "resold"
For the fully loaded G650, if it were flying, I'm gonna take a guess at $6 (and thats negotiating through the FBO).
[Edited 2012-02-13 19:16:38]