According to the Service Manual, all 4 SATA ports on the XPS 8930 motherboard are 6 Gbps. So you can use any of them that's conveniently located. You will need to get a SATA data cable for the new SSD, possibly one with a right-angle connector to the SSD and/or to the motherboard so it fits properly without hitting/rubbing anything else.  BTW, a caddy for mounting a 2.5" SSD in a 3.5" drive bay isn't very expensive, ~$10-$20, at most, if you decide to do it that way...
XPS 8930 - Replacing HDD with 2.5" SSD I need to replace my HDD with a 2.5" SSD. Can I install the SSD on any available slot? Does the location of the SATA cable matter? I do not want to buy a mounting kit. Please advise.
XPS 8930 - Replacing HDD with 2.5" SSD