Mate, thats dreadful luck, but depending upon your circumstances, I feel you are very able to fight it, at least to the extent that you can keep your licence. This all, of course, depends on your prior driving record as well. If you are a regular speeder (or should I say, get caught regularly), then no chance, but if your record is good, give it a try - its worth it.
For starters you are an experienced driver, with good knowledge of the road, its conditions, your vehicle and its capabilities, at a time of day with lighter traffic.
Add to this the government try and talk up speed cameras as a deterent and warning system, not as a revenue raiser, you could quite easily argue that getting done twice by the same camera in such a short period does not give you time to get your 'warning' - plus the fact that it was a recent change of speed limit.
I think as a minimum you could quite easily get one of them reversed, allowing you to keep your licence.
I don't for one minute agree with 'speeding', but I do believe one can exceed the speed limit and still remain safe and in control. I also absolutely disagree with someone who has a good driving record loosing their licence simply because their indiscretion happen to fall on a public holiday.
Best of luck!