William - got a chance to try out the code and it did have a positive effect but I am having a hard time measuring how much of an effect because I did a naughty change management thing and also updated my driver at the same time.

I am finding an increase in refresh time for all models (regardless of whether overlay/transparency is being used or not) after the driver update. LOL. So I now have to run some scenarios to reset my baseline with the new driver. But I have be able to show a positive improvement with your material definition.

Thanks again for your help.