Considering buying the Gigabyte GA-Z97MX Gaming 5 board for my next build, and I've noticed that it has a SATA Express connector - I've been out of the hardware market for a while, so SATA Express is new to me. I know the connector uses two SATA ports, plus the SATA Express, and it's electrically compatible with existing SATA3 drives, but would - for example, a Crucial M4 120GB - make use of the extra bandwidth?
Straight answer, no. it's akin to putting a 3Gb/s SSD onto a 6Gb/s interface where it doesn't make the SSD itself inherently different.