I would much prefer the 21st because I have to go back to Houston that weekend, but I'll manage somehow if you all decide to meet on the 14th.
I suggest Zilker Park, it's pretty central and there's plenty of parking. Or there's a small restaurant/country store in Volente at the beginning of Lime Creek Rd. I believe the drive at the last meet was Spicewood Springs? Is that a fun road, I'm not usually up north...