I'd also buy the 256GB SSD. Gives you more room to put your programs on it if you want, in addition to a slight speed advantage.
The 830s came 4 ways, the simple bare desktop SSD, the desktop conversion kit with screws, adapter plate, data cable, the plain laptop SSD and a kit with extra components if needed. Possibly there are similar packages for the 840. Just to be aware of. Sort of the same thing where you can choose a bare OEM HDD, or a retail version with the instructions, screws, cables etc.