I was visiting my local gun shop teh other day and really liked the 320.  The dealer only had black, and I was thinking about ordering the FDE version.  Without seeing one I do have some concerns
1)  How does the FDE slide finish compare to the Black Nitride Sig finish?  Which is better??
2)  The frame is FDE, is the plastic modeled in a FDE color.....or is it painted/cerakoted?
Thanks in advance

I have a compact 320 with FDE grip module, but a black slide. I'm assuming the FDE slide is cerakoted.

The Grip module is FDE plastic, not painted. FWIW, my black slide finish is bomber. I dropped the gun on asphalt from waist height (I know, I know) and it had what appeared to be scrapes in the finish along part of the milled cuts, and on some of the edges around the slide. I was bummed. Then I grabbed a rag and wiped it down. The slide looks brand new.

I have no experience with Glocks, but I bet their nitride slide finish is more durable than cerakote, if that is in fact the finish on the 320 FDE slide.

The grip panel is not painted and just molded in that color to my understanding. The slide is cerakoted, which is generally seen as less durable then the normal finishes as it's prone to chipping. It can be stripped and re cerakoted later in life if you want. It also should have the black nitrate underneath any way. I have a few cerakoted guns from sig and they are fine. If it was my gun I would choose the color I like more (FDE) and go with that since the 320 has the seralized part inside the grip anyway so later you can have multiple different sizes and colors.

The "Yankee marshall" on "You Tube" has that same set up.
He said the ceracoat FDE on his slide wore really fast. The Black slide finish held up alot better. Both were factory finishes.
The frames are molded in color so that doesn't matter.

I'm not sure what the FDE slide finish is, but it is not Ceracoat.  I've read that it is the finish is the same as the coating used on the Legion Series, just a different color.  Ion Bond?

So far, in my limited use, the finish on my FDE Compact 9mm is holding up fine to kydex holsters.

My P320 in FDE is holding up well. According to the Sig Sauer website, the specs for the P320 compact lists the slide finish as "PVD". Which I believe is Ionbond.

Like Cornfed stated my FDE 320 is definitely not cerakote but a PVD type finish. A close comparison slide finish is the M&P VTAC.  Not sure how it will hold up.  Here is a cerakoted slide against the PVD finish on the P320.  David