Benro KS-1 and A127n6 legset user here. I was very skeptical when my local camera shop recommended them to me, but they let me play with it for a good half hour until I was pretty dang satisfied it would hold everything I needed and then some. The price is good, the build quality is reasonably good. I have never handled a real Arca Swiss but this head does what I need it to. The real thing handles 90 pounds. Put it into perspective, even Canon's 1200mm MONSTER, the Beast Itself, is ONLY 36 pounds or thereabouts. I hear if you buy the Beast, they actually throw the tripod in for free. I have no idea though.. 
Anyway back to the question. I have been playing with my Bigma on this particular tripod setup and the images are coming out tack sharp. The Bigma is, naturally, my heaviest lens, so if it can hold that one steady, everything else (which is much lighter, I usually use my 5D and 17-40 for lowlight work, which is a fraction of the Bigma's weight) is fine.
The camera shop convinced me this was the one when they put a Nikkor 300mm f/2.8 and a big fat body on it and pointed it up at 45 degrees and it didn't budge.. I figure by the time I can actually AFFORD the Canon version of the 300 2.8, I can dang well afford carbon fiber and a real Arca Swiss 