What is the maximum capacity standard rotational SATA 3.0 drives I can install in the Main 4-bays in my Mac Pro 4,1 (early 2009)? The original Apple Spec sheets for my Mac pro states a total max drive capacity of 8TB (Four 2TB drives max). I am running Snow Leopard 10.6.8 (1TB Rotational) as a secondary OS and will be running El Capi 10.11.6 (1TB SSD) as the main OS. The firmware has not been updated to 5,13. I was hoping to install two 3TB drives (one for saving and working with graphics and video files) / one for Time Machine backup of one of my OS's and file redundancy from the first 3TB drive). If this is possible in this machine do you have any recommendations for what brand and models drives might be worthy of this upgrade? I'd prefer to use at least 7200RPM drives and I suppose a 64GB cache is fine if the drives are more economically priced but I am looking for good reliability. I'd prefer a faster drive as well but know there is a trade off to price and not sure if the 128 cache drives will make much of a difference in realized speed increase. Are there any performance advantages from brand to brand in the 7200/64 category and same for the 7200/128 category - Does one drive top the list on speed performance for a rotational offering? It seems like there are so many choices for drives I am not sure what to get to make it the wisest investment for my money. The goal is to find the best Rotational Drives for this upgrade to avoid the higher costs of a hybrid or full SSD drives. Thanks in advance for any help you can offer on this.