Significance of the memory clock?

I've been adjusting my msi r9 270 for a couple of weeks now, at one stage the card was quite stable at 1085MHz, but then i would get the blue screen.  I continually adjust down is periods of 10MHz and constantly get crashes, even down at 1035MHz.  Is having the memory clock at 1500MHz making the card unstable?

 

Are you sure its your gpu's fault for your blue screens? Is everything else stable - CPU etc?

High memory oc is most likely the cause of a cards instability. Its also the weakest link on modern cards meaning its easy to kill cards memory with high memory speeds and prolonged use. I would drop the memory back to default (1400 or thereabouts) then get your gpu core oc up again. If you start to notice any artifacts and/or graphic anomalies even at default settings then you've damaged the memory ~ RMA time.

Most of the time CCC will just have a tantrum and say the driver has stopped responding so forth...

Yes I think it was the memory clock causing the instability, i brought it back down to default and will start ocing again.  Its possibly my motherboard causing the restrictions on the memory clock as its very standard, msi h61 p-31

Your motherboard will not hamper a gpu's overclock. It just cant.

I thought that, just have to upgrade :)