I am looking for an ultralight tripod with the capacity to handle 8kg. I've narrowed this down to a GT1541 that weighs about 1.12kg and should be able to handle a 800mm (4.5kg), 1d3 (1.4kg), 580exII (.5kg) and a gimbal head.
The gimbal I am looking to attach the GT1541 is either a Wimberly II (1.4kg) or a Mongoose 3.5a (0.68kg).
Pao, I think your image quality would suffer with the 1541, given the heavy load you propose. Naturescapes Store recommends only up to 200mm for this tripod. Just because a tripod can support a load without collapsing does not necessarily mean that it will give you the torsional stability you need under that load to make sharp images. With that load, you should probably consider the 3000 series. I've tried using my 500mm/wimberley II/MkIII combo once on a similar model (1027), and I may as well have been hand-holding the rig. I love the light weight, but it's best for smaller gear and close-up macro work (2-3 kg).