guys its really simple.
if you dont venture out of office, mail, web browsing, you dont need 16gb.
if you're running some kind of proprietary application, vm, emulation, multitask you probably need 16gb, but can get away with 8gb if your system isn't under load always
if your system is always going to be on load, compiling, running proprietary apps, vm, you WILL need 16gb
the disk caching is not anything to worry about unless your SSD is always over 80% capacity + always under load + always getting extra r/w added. its not 2012 anymore, its actually really hard for 1 user to wear out NAND now. this is well studied.