tafreire :
I just want to know if is possible to use an U.2 SSD with SATA Express cable, no matter the speed.
If you can find a male sata express to female u.2, theoretically it should work, but you won't find anyone trying that and you're on your own in that experiment. If you're going to use the sata express cable you should just find a sata express drive, they will be much cheaper.