I think the problem is, that with all this stuff straped to your bike, you shouldn't try serious mountainbiking
. I once tried it and it was terrible!
If you want to take your stuff for an overnighter, then don't leave the gravel forest roads.
If you want a singletrail ride, only take smallest possible amount of gear in a small pack.:You_Rock_
And check out on various MTB forums about disc brakes! There are a lot good ones, as long as they're hydraulic and have big discs (180mm and 203mm are common in Germany). In Britain they often sell them only with 160mm!
That's ok, if you do -50m on one run, but for longer downhill sections: They don't stand it:BlueTeamE. Look at what they use around the alps!