Chiming in, yes the autofocus on the 80-400VR isn't super-fast, but it's not that bad, and it works better on some cameras (D2X, F5 or F100) than others (older Nikons). More to the point, this is also a relatively slow lens, so you can probably forget freezing birds on the wing or a big cat bringing down its prey at 1/1000 anyway, unless you're willing to kick your camera into the ISO equivalent of 1600 or 3200. So what do you need superfast AF for?
If your main interest is underwater photography (in which case you're already going to be overweight with photo and dive gear on your flight to Kota Kinabalu), do you really want to bring a f/2.8 400 weighing 3 kg (or a 600 mm f/4 weighing 6 kg), plus a big tripod steady enough to support it with all the rest of your gear, or shlep it with you trekkiing through the Borneo jungle? Not me.
At 1.2 kg (without the tripod collar), the 80-400 VR, for what it is and what it does, is incredibly small and light. You really can hand hold this lens at 400 mm, which is pretty amazing. Even at f/4.5 or f5.6, you'll probably be shooting at 1/125 or even slower, so the optimal subjects are going to be fairly static - birds perching rather than on the wing, an orangutan peering down at you from the trees rather than freezing a big cat running or in mid-air. You'll learn to live happily with that, and you probably won't be bothered by the slower AF. In low light, you'll probably want to use MF anyway.

Lilac-breasted roller, Kruger National Park, SA. 80-400 VR.

Cheetahs, Hluhluwe Game Reserve, SA. 80-400 VR.
Frogfish (Robert Delfs)