Discs add hardly any weight, I've weighed. And V-brakes don't clog up unless you are going through knee-deep mud, but they only make noise as they usually rub the mud off.
Suspension adds a bit off weight, but it's the spongeyness that takes away all your speed. Try tighten it up to a suitable weight, or lock it fully. Rear suspension is pointless too, unless you are doing big air jumps.
But I don't know much about Mountain Bikes, I do velodrome, road race and time trials sometimes.