Mutt, These range numbers are all based on a full fuel load of 44,200lbs. Typical BOW numbers for a G650 are in the 54,500 to 54,700lb range, subtract that from the 100,000lb max ramp wt and you get a payload of 1,100 to 1,300 lbs.
The 650 can carry up to a 6,500 lb payload at lower fuel loads and lower BOW's (Max zero fuel wt is 60,500lbs)
If you really wanted to fill all the seats (typically 16 to 19) then one could still loft over 42,000 lbs of fuel which would shave off about 1 hours worth of cruise time at M0.87 or roughly 500nm (typically see fuel flows of 2,000 pph or less at the lower weights), so it wouldn't be unreasonable to expect around 6,500 nm in that case.
Solent, sorry to hear you had a bad experience with the G200, I flew an Astra for a few years and found that Gulfstreams support of that "Bastard step child" was also very good.
The majority of my flying is between Japan and Europe and I have found the response of GAC in Luton and Basel to be very good, dispatching techs to make on site repairs when we needed them in Frankfurt and Nice first thing the next morning. About the only gripe I can make about support in Europe is the apparent reluctance of personel at Luton to work overtime. (Something to do with that British "Got to have my 5 O'clock cup of tea" mentality?)