Yep, pretty close. Just off the top of my head, 30 cubic yards (24-26 cubic metres) would roughly equate to around the 20-24 tonne mark, though the discrepancies of moisture content in the opal clays and sandstones along with the hardness can cause it to vary quite a bit. The cubic area removed is generally taken as a 3:1 ratio when loose, which seems pretty right too when we've looked into it on and off for yardage.
Our old mining partner, John was a shovelling champion here from the early 70's right into the late 90's. He comfortably won all the comps against the other miners every year -back when they were all real workers unlike today where they get tired just from pulling levers on a digging machine. 
He taught me the ropes and how to develop good technique from my very early teens and that eventually culminated with me pushing three (what I would consider) record runs here between 2005-2007 on days where I was working solo and feeling good, also knowing that I didn't have to stop to gouge as I was only putting in long prospecting drives looking for a change in the country.
My third and last "attempt" was back in early August of 2007 (the first Sunday if memory serves?) and was my best, but not by much due to the sheer mechanical hoist restrictions outside of my control. I ended up pulling out thirty cubic yards (three ten yard trucks full) in one hour and forty five minutes from a depth of 47 feet out at a field called Dentist Hill. I was about twenty feet in away from the hoist when starting, so quite an easy back and forth with the rickshaw. Most of that speed simply came from my good jack hammering technique and having a very hard hitting Kango hammer. The shoveling was always the easiest part for me, thanks to John, so that was never the issue. The ground there was fairly hard up top in the level, just under the roof at around head height, but manageable. The drive I started at 11am that morning was fifteen feet long by four feet wide and six foot six inches high when finished and I was back home again for lunch by 1:10pm.
Hope that helps shed a bit of light on the subject, Mackka. I wish we had the current phone camera tech back then. I'd love to have those runs on video, alas they're only my recollections of glory days gone by now. I certainly think I could still come pretty darn close to those times today, despite a bit of age and physical wear under the belt. The hardest part now is finding a good, solid hoist that would stand up to that work pressure. They just don't build them like that anymore sadly. I still have my eye out for one that I may be able to modify however? Who knows...
Cheers,
Shauno.
