We did Mersey Crag/Turrana Bluff from Little Fisher River track a couple of weekend's ago. As Lucas said, it's a fair distance to cover but the majority of it is disused firetrail from the car park to a couple of km before Rinadenna Falls, so it's fast and easy walking. From the Falls to the very top of Long Tarns (the southern ridge where both Abels can be best accessed) is tighter single track that does get a bit vague in places, but I honestly can't see coming through the south being quicker.
About the only tricky part was crossing the Little Fisher River itself. The marked spot just below the falls was pumping and the couple of spindly trees thrown over didn't look safe at all. I ended up doing a little impromptu bridgework a couple of hundred metres further downstream with a few shifted boulders. The water level had decreased significantly on our way out two days later, however.
Really is a wonderful spot to check out, hopefully you'll have great weather as the views are amazing.