, I can help answer your questions.
I've done many upgrades to SSHD's and I can tell you that the performance is great. My boot up time went from 90 seconds to 30 seconds. Also, programs responded much faster because SSHD's including the one you are looking at have great performance. The difference of 8GB SSD caching won't hurt since the actual SSHD is a big memory chip as well which offsets the 8GB SSD cache. It's a great drive.
Thanks very much! Do you have any information (as specified in my original question) on whether using my SanDisk ReadyCache with the 4TB/8GB SSHD would be beneficial, problematic or even possible?