Got a Late 2013 iMac and 16GB of DDR3 2400Mhz ram.. can this ram work in this iMac? Right now it's DDR3 1600Mhz.. I know I probably wont notice a damn bit of different but hey why not install it right?
It should work but as stated above will run at the normal bus speed of the iMac = 1600MHz. If it kernel panics after installing the faster memory, then you'll know it's not compatible.
If this is desktop memory then no. The iMac takes 204-pin DDR3L (low power/laptop form factor). As far as I'm aware the best DDR3L RAM available is 2133 MHz, which works fine without down clocking to 1600 MHz.