I find that the water levels in the Colo are best treated as relative. At some points years ago they used to be around 0.30m, so 0.55m would be a good level to lilo at. At the moment, 1.00m would probably be quite good. You'd need to be watching them for a while to get a sense of what "normal" was.
I generally allow 1km/h for paddling lilos with low flow.
Your main issue will be that once you round the bend of the Colo, it's sand from bank to bank, and hard to find the deepest channel. You will probably end up getting off and walking at times as you run aground. You probably won't be running the rapids either at 0.75m.
For speed comparison, we were walking upstream from Colo Meroo to Tootie Creek at about 2km/h. Downstream, the going might be a little quicker (2.5km/h?), since if you're walking in the river, the flow is helping, and if you're walking on the bank, the vegetation is pointing the direction you are going. So you can always make up time just by getting off and walking!
You can see some recent pictures to give you a sense of river depth at:
https://photos.ozultimate.com/Bushwalki ... colo-river