CoD has implemented hardware texturing and lighting, which has considerably less drain on the engine. So, yes it does aid performance, particularly with large outdoor maps. The downside is that it means you need a halfway decent graphics card. Nothing exotic, about NVIDEA TNT2 class. Most graphics cards have supported this for a few years, but the original Q3 was developed at a time when a lot of cards didn't.
It will be some time before these maps are functioning in CoD. Between the Swamp and the Jungle maps, there are about 5000 patch meshes, which don't convert to CoD, for some reason. Fortunately, they are reduced complexity meshes and are not difficult to recreate, but when you have that many, it still takes time.
I have also begun work on a remake of the 1993 PC game of the year "Alone in the Dark", using the CoD engine. It's a single player game that takes place entirely in an H. P. Lovecraft style haunted house. So it's only one big map. It has always been one of my favorite games and there are many younger players who have not seen it. This was one of the first "3D" games and the graphics and player models, while state of the art at the time, are pretty horrible now. The preliminary mapping work I've done on it so far looks very promising. It's going to need some very moody custom textures but it should be a "kick-ass". Here's a link to this game if anyone is interested:
http://www.adventurecollective.com/reviews/aitd.htm