Have driven Hummers in Aus and they don't seem particularly good. Whilst they are capable of some interesting offroading, the load capacity seems to be fairly limited due to the high transmission tunnel and I think 80 mph is probably unrealistic.
Currently have a 110 Defender which we have driven round Aus / from UK - Cape Town. Its fully kitted up and its quite good. However I think we are going to head in two directions.
As far as major expeditions go, we are lookin at a Bedford TM, these come in both 4x4 and 6x6 format. They have full diff locks and are quite capable. Whilst not as capable as a mog, they have a lot more load space than most mogs and cost less.
As far as replacing the Defender goes, we probably won't do it for a couple of years but looking at a 100 series Landcruiser. They are all over the world, so fixing them should be relatively easy including getting parts. They have way more power and comfort than a Defender and similar offroading capabilities. The two downsides are they cost more (although One can spend a lot more modifying a Defender to get it to perform in a similar manner, eg improving 300TDI engine, fitting cross axle diff locks where they can come as standard on some 100 series, etc). The other obvious downside is looking like you are worth more than you do in a Defender and potentially attracting the wrong type of attention. However lots more comfort, easy cruising, just as capable offroad. Defender would be my second choice ahead of the 78 series.