The reason I asked that question was bcoz I use 055XPROB but it is build to handle only up to 15.4lbs (7kg) load ... but the 393 Gimbal Head is built to carry up to 44lbs (20 kg), so isn't that kinda mismatch? Ideally one would want to buy a tripod and head with identical or similar load capacities.
Are you referring to 055XPROB?
Either. The ergonomics are different between the two, but the basic build is the same.
I much prefer the ergonomics of the 3021BPRO, especially the fact that I can quickly completely remove the center post, making it really easy to basically convert it into a tabletop tripod. I seem to remember having better options for hanging a weight off of the 3021BPRO for additional stabilization, but I wouldn't swear to it.
But both will support the heaviest of loads equally (very) well.
Of course, I have to admit that I don't know the load capacity of 3021BPRO
A quick search suggests that the 3021BPRO has an official load capacity of a bit over 13 pounds.
However...that doesn't seem to have much bearing on anything in reality.
I've often put the post horizontal, extended all the way, with a gripped body and medium telephoto (such as the 180 macro) pointed straight down, and a lot more than 13 pounds hanging from the center to keep it from tipping. Never even a hint of a problem, except that you have to watch out for vibrations...I only do this in the studio with flash, where not only is there nothing to cause vibrations but the flash itself eliminates the problem.
I suppose in its least sturdy configuration...say, legs fully extended and fully splayed, with the center post sideways, then it might have a problem with a 13 pound load...but, even then, such a failure would really surprise me.
That, and it's a bit of a challenge to get a load that heavy in the first place. The 400 weights 8 1/2 pounds. The 5DIII is another two pounds; with the grip, it's three. The Wimberley head is three pounds, which brings you right up to the official limit -- and, again, my setup is so rock solid that it wouldn't even occur to you that there's even a theoretical possibility of a problem.
Lastly, manufacturers are notorious for specifying bogus weight limits. For example, RSS conservatively rates their BH-40 at a mere 18 pounds, even though it'll support twice that without problem. It just won't be a very pleasant experience working with much more than a 300 f/4 on a ballhead that physical size. The competition would go ahead and rate a similar ballhead at 35 pounds.
For me, that's what the 13 pound specification means for the 3021BPRO: works great with a 13 pound load -- and it does. If you're regularly going to put a heavier load on the legs -- such as a studio video camera -- then the tripod isn't for you. But you're also not looking for a tripod such as this in the first place.