For most australian 4x courses you don't really need suspension, let alone a dually. Though it's a requirment to have some kind of suspension.
If you've never raced 4x before, you'd be better off picking up a cheap 2nd hand hardtail and having a little fang around at a few races and see how you like it.
But it's your money and because i'm such a nice guy ill help you spend it.
you want a light weight, nimble frame.
Banshee amp is very light at 2kgs. But it has horizontal drop outs
Yeti DJ is just epic, can't go wrong.
forks, you should only need 80mm of travel:
Rockshox reba, light xc forks, you've got to learn to ride smooth but they should hold up.
Or Fox F80's.
wheels - Hope pro 2 on mavic xm717 or if you think youre a bit of a hack get some ex721's.
Brakes - Avids are good, juicy 5/7's if you want a little less weight and spend less money. Or elixr's if you want more power. You should be good with juicys though
Shimano XT's i reckon have a really nice feel and are quite light, though not everyone likes them.
Other stuff - Shimano SLX cranks, saint derraileur, xt shifter, gamut chainguide, Easton EA70 bars and sunline stem. Maxxis larsen tyres.
But seriously, give it a go before shelling out.
