LOL, Awesome, you lot come to my backyard the weekend I'm racing at OP. oh well, shit happens.
My suggestion,
Head up Bells to Lithgow, lunch there would be the option if you leave Homebush at 11am, would make it around 1:30-2pm lunch. IF you can get away earlier then continue through Lithgow and head back towards Sydney for about 2kms on the highway. Then take a right out to Tarana where there is a ripper Pub to stop for a bit, kick arse steaks and pretty cheap too!
From there head back through past Jenolan Caves road, to the highway. Head for Sydney again to Katoomba, where Cliff drive down to Leura is a must do detour!
Once you rejoin the highway again then head down to Springwood, where you will find Hawkesbury rd on your left (I am forced to travel this road daily on my way to work) where you will find a 3.5km hill climb section about mid way along that I would kill to close and have a red hot go at hill climbing one day. You guys will be travelling down, but it is worth turning around and heading up just once, windows down radio's off, and there is a nice lookout at the top for a stop. Just don't go up and down too many times as the heat will make their way out eventually if you do.
Continue along this road and head for Richmond, and then head home the way you came.
Hope this helps, and that should keep the drivers amongst you happy!, heard that the Tarana road was recently resurfaced, so stiff springs shouldn't kill you any more.
Cheers,
Dan.