I have both the Velbon El Carmagne 540 and the 630 very much like them.
I have used the 540 for 35mm, medium format, 4x5, and a Nikon spotting scope. With my EOS system, I have a 400/5.6 and it handles that just fine as well. With the center post extended, the 540 might seem a little precarious with larger items but I haven't had any trouble yet.
The head that comes with the 540 has turned out to be a good tripod head for me. It's a basic tilt and pan which I prefer to ball heads. It's not a quick-release head either but works with all my gear w/o investing in plates.
The 630 being taller is more comfortable to use, particular with things like large format cameras or big lenses/scopes. It's a tilt and pan head is larger and better suited to medium and large format cameras than 35mm. However, collapsed it's a bit longer than the 540 and about a pound heavier.
Between the two, I use the 540 more because it's lighter and less bulky, but the 630 seems a bit more stable and nicer to work with when set up.