I have the Goliathus and I got the extended which works out great for my set up , speed pad,keyboard and mouse all fit on it and the surface is just right for gaming.
The mouse has multiple dpi settings and they all work to perfection on this surface. Best mouse surface I've had and it's washable with a rubber backing for non slip.
The Sphex looks good and has what looks like a hard surface and is very thin. It has a stickey back for non slip but that may wear out over time and become less stickey.
Given a choice between the two I will chose the Goliathus pad for it's weaved surface and rubber backing.
It would be interesting to see which one wears better. I've had mine now for over a year and have just washed it and it's now like new so I'm anticipating this lasting at least another year and if it does I will be very happy with that time frame.