Well just had a failed attempt to add him to the 6ft. The jungle perch tried to beat him up, I gave it 10-15 minutes but he's back in the 5ft now recovering, I'm hoping he's ok.
Measured him just before I added him back to the 5ft and he's now 22cm which is great and he's noticeable growing fast now that he's into his food more.
Next attempt might be with a divider, or just wait until he's 30cm+, we'll see.