Due to the importance of the min and max samples. Is there any way to pull any stats at all on a render that can inform you if you are under sampling an image or oversampling needlessly. I know brute force is the flavour of the moment but a little tuning can make a big difference with render times.

Rob

have a look AOVs provided through VEX Variable dropdown menu in Extra Image Planes tab on mantra

Direct Ray Samples
Indirect Ray Samples
Shading Samples
Opacity Samples
…

they will inform you about how much samples which area of your picture uses and other things

As far as I can see they don't actually if your oversampling. Correct me if I am wrong

not sure what you mean then
if you keep your min samples to 1 and let noise level take care of your max samples, you should hardly oversample due to Ray Variance

however if you force oversampling by blindly upping your min samples, pixel samples or light samples to begin with, then I'm not sure what you can use to tell you that the amount of samples is unnecessarily high for certain areas, I guess its mostly about carefully increasing correct samples in correct order as guide suggests
http://www.sidefx.com/docs/houdini14.0/render/noise [sidefx.com]

There is an image plane preset called “Ray-level” which gives you information about the level of noise in the image. From what I can gather pure white values in this plane mean the renderer hasn't completely satisfied the noise threshold and could use more samples.

Over sampling should be automatically prevented with the ray variance antialiasing. You can set your max rays to something very high but the renderer won't actually use them if it's not necessary.