I found out a few fascinating things while trying to make sharp pictures at low shutter speeds and high magnifications. Heavy isn't enough. My first tripod was an 8 pound Gitzo. Even using the mirror locked up it wouldn't allow a good sharp picture with telephoto lenses. Any small vibration would take forever to settle down. I then tried a heavier 12 pound Bogen 3051. This tripod was fairly loose at it is pivots and joints but it was a lot  less susceptible to camera or wind induced tremor.

Try this easy comparative test. Mount your longest telephoto lens on every tripod you are considering. Extend the tripod legs to their complete length. Do not raise the center column of the tripod. Whilst looking into your camera's view finder, give the legs a really mild slap with your hand. Watch and see how much time the picture in your camera's view finder "jiggles" or oscillates around.

Pick the heaviest tripod that you simply can stand to carry that gives the least quantity and duration of image "jiggle". Should you continuously need to adjust the back and forth tilt because the composition inside your viewfinder changes as soon as you let go of the digital camera or tripod controls, the tripod is sagging under the weight of your lens. Unfortunately, using a heavier tripod is generally the only way to fix this issue.