How Many HDDs On A Cable?

All PSU SATA power cables I've seen have only four connectors on each cable. Assuming the rail can handle the load and the wire used is large enough to avoid a voltage drop, is there any reason why there can't be more than four HDDs on a cable?

What I am wanting to do is run an SSD (boot/program) and six data drives (probably 2 TB WD Greens) on a single cable that I can make up (the PSU is a modular Corsair HX750; a bit oversized but that will cut down on heat and, hopefully, increase the life of the PSU) to cut down on cable clutter (the case I want to use is a bit tight; space to put it is a problem so it needs to be small). The original cables are made with 18 AWG wire. By using #14 AWG wire, the calculated voltage drop at the last HDD in the string (the SDD would be first) will actually be less than on the Corsair cable. The computer would read or write to no more than two of the HDDs (and the SDD) at any one time. There will also be two hot swap bays (3.5" and 2.5") in the computer (for making back ups) as well as an optical drive but each one of those three will get their own cable.