To save me searching through 100's of posts, can anyone tell me what the performance of the 73/9s is like now? I know there were some serious doubts about whether they would be suitable for the job or not, so wondering what the current status is.
That good they still use a 67 on the Inverness.
In fairness the 67 is being used as it's the "courtesy loco" to cover the absence of 73969 whilst it's being repaired after VTEC rearranged one of the cab ends of 969 in Craigentinny in Dec 2016. The Inverness will have 2x 73/9s on in due course, so makes sense to use the 67 (solo) on this portion as means only 2 other 73/9s are needed for Aberdeen/Fort William - handy whilst locos are still going through Brush for the mods (as per
@ScottDarg 's info).
969 is due for release imminently and 970 not far behind, so I suspect it will not be too long until the 67 returns to DBC and the North of Edinburgh portions are 100% 73/9 worked.
In terms of your original question, the 73/9's performance outside of leaf-fall season is very good; in leaf-fall season it's not great at all! The 73/9s suffered repeated wheelflats in the Autumn and at one point there was only one working with round wheels. I fully expect GBRf will not be sitting on their hands with this, though, and will be looking at ways the issue can be mitigated ahead of next Autumn.
Prior to the trials of Autumn, Caledonian Sleeper was top of the PPM charts for two months running (across all TOCs) - more impressive considering how one service being significantly delayed can disproportionately impact the CS figures for a period. This performance wouldn't have been achieved if the 73/9s (and 92s) were still being iffy.