Well, PI is being over-used and in my opinion it's a horrible base if you're experienced. However, if you're a starter, I would certainly recommend it.
A lot of played servers are 667 loading higher revisions, you might want go with that.
Don't go with 508, how much I love them though, it's like not-used.
Finally, if you want to go for a 317, I would recommend you "Niobe". It's a custom framework and it's really well programmed. Lot's of stuff has to be added like weapon stands, emotes, gfx etc! so you can do lot's of work. It has pretty high graphics and a good packed, small cache. People like small caches, trust me.
Niobe download urll
Hope you use some of my information. ;-)
EDIT: Forgot to mention your 2006 era,
A lot of 2006 re-creation are out. Are you really going to be unqiue when you choose to do so?
There's plenty of clean sources in the download section, you can find one yourself. ;-)