You guys made me look.
Here is some quick actual info, see the attached pictures of the Gitzo 1541T and Sirui 1205X
I never tested them with the same setup as I'm using for different purposes but I just put them side by side.
The Gitzo seems to be a touch more stable when trying to rock it around, not really scientific. The difference is probably more to the fact that it has 4 legs vs 5 legs on the Sirui.
The articulations are stiffer, could be because is older. The Sirui has more meaningful hard stop angles, 1 extra vs Gitzo.
Easy opening, they are similar.
The Gitzo gets a touch higher, particularly with the column extented (I rarely do).
Sirui is a little lighter by 70g and is significantly more compact when folded, 13.8" vs 16.1".
Theoretical supported loads: Sirui 10kg, Gitzo 8kg.
I got the Sirui because it gets more compact. If I don't need the compactness (it comes handy even when is not absolutely necessary) I usually take the Gitzo. These days if I don't care about the weight I get the Manfrotto 190CXPro (I think that was the name) that is more stable and has a column that get horizontal.
If I had to choose again I would look at the Sirui T-1204XL. Is as heavy as the the Gitzo at 1 kg but gets taller at 52 vs 44.5 (w/o column) and has a better weight rating at 12kg for whatever it's worth. It's less compact at 18.3" though.
This Sirui sounds practically as good for a better price, not that is that cheap at 370$.