I think this is the route I will go , after a little bit of thought , I concluded that with my setup of 2 SSD's , the 80mm case fan and a tall heatsink, I would benefit more from just trying to keep everything cool rather than just having the fan work when the CPU is getting a little hot.
I'll have to do some testing to discover the most optimum setting for the fan to keep everything cool but not too noisy.
I am however , still intrigued with the overlay concept and so I will be doing further research into this as I think its an interesting topic that I haven't really given much thought to before. I've discovered that it features quite heavily when you begin to get serious with arm based SBC's and therefore will prove useful in learning.
Out of interest @soerenderfor what value did you find worked for your setup to keep the temps that low with such a full case ?
I decided on the Marvell 88SE9230 this one to be exact
I hoping, although I haven't done any serious testing, that this removes the errors I was getting with the pine64 PCIe card, w hich eventually mounted my drives as read only, before remounting them as different drive devices.
thanks for advice , much appreciated .