Ideally you want them about a foot apart, in practice - for 4 feet - go right ahead and zip tie them together.
Whilst this may seem like contradiction, the IEEE specification for installation of data cabling does provide recommendations which are based on the voltage levels in the AC power cables, you'll find that almost all the cable management systems designed for server room rack installations, lump all the cables going to any given server into a single bundle - right at the very end, where it runs through a "cable management arm" and connects to the server.
The "cable management arm" is a hinged frame with one end attached to the rack, and the other to the server, and allows for the server to be slid in & out of the rack for service access, without disconnecting the cables.
