I personally haven't been out of Tannum sands though have out of 1770 many times, Fitzroy and Sykes is accessible out of both, Bundaberg would be a serious hike and more likely done in a big boat like a liveaboard (I did this once on Big Cat Reality when it was a dive boat).
My understanding is that Tannum sands has it's own issues with low tide, ie the ramp isn't accessible at low tide simply due to the size of the tides up there. Though if someone who knows Tannum Sands could advise if this is correct?
We have always been able to get in and out of 1770 however last year we walked the boat through the shallows to get home.