Ken, Sorry to have to tell you that my figures are correct. It may well be that the base ac theoretical weights give the possible "substantial" payload that you refer to but the figures that I have used are the practical ones. It's a bit like the theoretical max fuel of the Tristar KC1- not possible to achieve on a day to day basis.
OK, your fuel and weight figures for the Voyager are correct. So? It's still an odd design that makes it impossible to put on a full fuel load (on the other hand, if the Voyager's max ramp weight is 3t higher than MTOGW then the crew can burn off 3t of fuel before taking off. Still kinda odd though.) However a number of folks have stated that the RAF's other air tankers have belly tanks with the TriStar's belly tanks having near 100Klb capacity. A "standard" A330 cannot reach MTOGW with just fuel, and you never answered if the RAF did or did not put belly tanks in the Voyager to enable it to reach MTOGW with just fuel. Just This Once in post #93 implies that the Voyager, unlike the other RAF air tankers, has no belly tanks. If that is true, then either the Voyager's empty weight is 20Klb higher than a "standard" A330, or either the fuel capacity figures provided by both Janes and wiki are off by 20Klb, or the figures provided by you are off by 20Klb.
This much I'm very confident of: the MRTT offered to USAF did not have belly tanks and it could not reach MTOGW with just fuel. I have no idea why the Voyager is different in that regard. I also have no idea why that difference is so important to some folks that they've gotten their knickers in a twist over them. But here we are.