I've stripped down the O2 chassis to find the cause of a slight bind (this was the reason it wasn't released to traffic at RailEx) and took the opportunity of changing the bogie pick ups to something much cooler I saw on the Scalefour website forum. Basically, it uses Alan Gibson sprung plunger pickups bearing on a gapped copperclad stretcher to transfer power from the wheels. The two plungers also mean the bogie is sprung. Pick ups from 36swg phosphor bronze were added including a link to the back of the plunger. Lots of loops to allow for movement.
There is virtually no resistance to the bogie (compared with the previous wire links). Bus bars from 0.3mm brass transfer feeds along the chassis. I've since put the body back on and pleased to say the whole thing now runs much better. I'm really impressed with this system and will be using it for other engines.