Eyefinity and Nvidia Surround are extremely flexible systems, able to handle any mainstream monitors natively at the frequency required. Obviously, the higher the resolution, the worse the performance will be, but both setups will work.
Eyefinity can support a greater range of monitor setups than Nvidia Surround, but I am only testing 3x1L here which all 3 systems support, so I don't have any extra data to add to this.
The Matrox Triplehead2Go is limited to 5040x1050 at 59/60Hz (the site says 60Hz but has a disclaimer to say it may actually be 59Hz, which it is for me) or 5760x1080 at 50Hz.
To understand why this is, you have to understand the Matrox setup. It only uses one video output from your graphics card to source the whole image and a USB cable to control the box. You then plug 3 monitors into the Triplehead2Go box. The dual-link DVI connection on the box and your graphics card has a limited bandwidth of just 7.92Gbit/s, and at these resolutions it is absolutely maxed out. In fact, from what I have researched, it appears that it can only support 57Hz at 5040x1050 and the last 2 frames per second are sent via the USB cable.
This is not a huge problem for 3 x 1680x1050 monitors as nearly all of these monitors will support 59Hz, but it is a problem for 3 x 1920x1080 users as not all monitors will support 50Hz. And if you use larger monitors like 1920x1200, then forget it.