To follow up on my original post.
I'm running FreePBX 2.7 on my own build of Asterisk 1.6.2.6.
The only problem I came across was a double quote issue with the Fax Configuration module. I tracked it down and fixed it myself, then discovered bug 4099 covered it and the next day the Fax Configuration was released with .17 and the fix.
The only other issues was that, 1.6.2.5 worked with spandsp 0.0.5 only, and now 1.6.2.6 works with 0.0.6 only. Wierd, but, whatever! Faxing is working 100% and I absolutely freaking LOVE IT.
The other new features in 2.6/2.7 are just lovely as well. Virtual extensions, more queue control, pinless dialing, allowing faxing to every extension with a separate email as a destination (HEAVEN!) .. loving it.
I have one box running PIAF & 1.4 with FreePBX 2.7 and two boxes running handrolls of 1.6.2.5 and 1.6.2.6 with 2.7.. they are all functioning great.