To me, then, that eliminates dual-suspension bikes. I think I'd still want a front-suspension fork, but adding a bunch of pivoting parts in back just makes things too complicated. In terms of the ideal bike, I happen to think the one I ride most weekends, Marin's Pine Mountain, would do the trick. It has a steel frame that's tough but also more forgiving than aluminum, so you wouldn't miss the rear suspension so much. Price is $1,700. Kona's Kula Deluxe ($1,899, www.konaworld.com) has similar specs with a lighter but still tough aluminum frame, so also would work well.
In either case, I'd consider a few retrofits before embarking for East Africa. I'd probably put tougher wheels on both—pair of Sun Intense Mag 30 rims in the 36-hole iteration, laced to Shimano XT disc hubs. You'll probably pay about $300 for a pair, and it would put the odds you'll break a wheel down as close to zero as possible. You might also swap out the hydraulic brakes on both bikes for Avid mechanicals ($100, www.sram.com), eliminating the risk of an oil leak. And a high-end fork such as a Fox Talas RLC ($600, www.foxracingshox.com) would be a worthwhile upgrade.
I don't see you loading the bike with your gear—it would be difficult to attach it in a way that wouldn't upset the bike's balance. So I see a trailer in your future; probably the classic B.O.B. Yak trailer ($299, www.bobtrailers.com). They work well on trails and are rugged enough to withstand a tough trip like the one you're apt to have. I've pulled one for years when road-touring, and have seen them used successfully on singletrack tours of the Continental Divide.
Ready to see the tricked-out, bump-eating future of bikes? Then check out "State of the Art" from the April '05 issue of Outside.