Far south west. Toolum forest, Urbenville and Old Bonalbo.
This is about as far south west as many people will wander to in a day and there is a couple of good rides nearby.
South of Queen Mary Falls is a nice run up or down the mountain and then you are at Legume and the terrible road from there to Woodenbong is barely passable being so rough it will bottom out suspension and probably smash fairings on sports bikes.
If you take it easy for a bit then you can turn off and ride to Urbenville via Toolum Forest. This road is still mighty bumpy in parts but no where near as bad as the other and you climb a nice hill with great views and ride via a cooling rainforest section before dropping back down to close up views of the huge rock formation that is the backdrop of Urbenville and the final run into this sleepy village - that has premium fuel! (behind general store) Map
Returning towards Brisbane you need to ride first from Urbenville to Woodenbong and this is a nice flowing little ride. Road is in good order with plenty of corners. From here you ride the fabulous Mt Lindsey range NSW section and then (for me at least) the equally enjoyable QLD side, see my post on these roads elsewhere.
Urbenville to Old Bonalbo seems also popular with bikes. Very bumpy in parts and new road elsewhere this is not a bad ride through another forest and its a good way to head if continuing further south. But possibly heading this way will be too far for most so do the maths on the return ride time from here beforehand (you can actually ride to Tenterfield and back in a day no probs) Map