Hello Dr Zoos, As long as you are at 3500' you should be able to glide to land between Moreton and Bribie Islands, assuming a ten to one (or better) glide ratio.
Tracking direct from Murwillumbah to Hinze Dam Wall, you should see a saddle in the range. This would be the safest track. If the weather is not agreeable I would be prepared to turn back to Murwillumbah to consider plan " B".
When you are over the range, you don't need to go right to the dam wall, but make sure you are well clear of Gold Coast CTR and at no more than 1500' when you track to Q1. Tracking up the coast, give a radio call on 119.0 for traffic at Seaworld, Mason field and Heck field. If you fly low level up the coast, give a call on 126.7 for Tangalooma. The recommendation is for north bound traffic to track up the eastern side of Straddie and Moreton. Hope this helps. Regards, Bob