In theory the WWX is a 3-days conference with workshops on Monday, which are usually attended by no French people except some of the guys involved with Silex Labs. Given the choice to go back to work on Monday I might do the same, but as one of those traveling in from quite a bit further away, I don't have it. So personally, for the reason Daniel pointed out, I find May 23rd quite an interesting option. It's that one time of the year where we all get together.
But that's just an idea. I have no interest in spending the workshop day surrounded by a bunch of French people angry at me because I suggested stealing their 3 day weekend :D
As for June 6 I think I remember we already spoke about this last year or before: It's a bit problematic in that in many countries that's already in the holiday season, which will make it quite hard to come for some people (IIRC Franco pointed this out last time).
In the end I think whichever weekend allows fixing the date as soon as possible will be the best, as that gives everybody more time to arrange themselves.
Best,
Juraj