maurice said:
So he can have a nice, light, good handling mountain bike when he wants, then put the panniers on and have a reasonable weight touring machine when needed?
Fairly obvious.
Ok, I've gone that extra bit and looked up the weight of the Trek6700, it's claimed at 27lbs, but you'd have to add the weight of the rack. so let's assume the OP is looking for a MTB come commuter/tourer that, depending on setup, can weigh in range 25-30lbs. I don't know how important front suspension is to him but I'm building up a 29er, no suspension, at the moment that ticks the other boxes.
Surly Karate Monkey frameset, with rack, single chainring and 9 speed cassette comes in around 28lbs. This is with Mavic A719 rims, Deore hubs and gearing, Marathon Supreme 700x50mm tyres, flat BMX pedals, etc. You could trim the weight a bit on the parts but may want to add a bit back on with bigger/knobblier tyres and maybe a rim like the Rigida Sputnik. Cost to build would be between £800-£1000 without going crazy on the components. I already have most of the components and am just moving them from another frame.
But I'm building this with road, light trail and backup commuting duties in mind, a general all rounder. So I've not really looked too hard at off road handling and capability as I'm not planning any technical riding. Hence no need to look at front suspension. For any lengthy road rides, or touring, I have more suitable bikes. But the KM should work well as an all rounder and has a pretty long effective top tube, something I needed.