DNG Codecs and EM 2

I'm confused about the role of and need for DNG codecs in EM 2 for Windows Vista (and XP).

I've just installed EM 2, and I can import DNG files and see full-sized previews (when "Use embedded previews when available" is checked in Preferences).

I briefly tried EM 2 Beta, and I believe that required a DNG codec to import and see full-sized previews. Has that been changed in EM 2 post-beta?

I did install both the Ardfry and Adobe Release Candidate DNG codecs on my machine, but then removed them, so they're gone as fair as I know.

Will these codecs add any funtionaility to EM 2?

My initial disappointment with EM 2 is that it is noticeably slower to display full-sized DNG previews. IVMP took maybe 0.5 second, EM 2 seems to take 2 seconds -- but this is a real pain when trying to quickly page through and compare many images. (That speed with DNG was a key feature of IVMP for me.)

The speed is even worse with PSD files. A 150 MB PSD file on IVMP took about 3-4 seconds to preview, versus 12-13 seconds on EM 2. Ugh!

I'm using Windows Vista Ultimate on an Intel Quad Core Q6600 with 4 GB RAM and a mid-range graphics card. This slowness will move me back to IVMP for now. The images are on SATA hard drives in an external SATA box connected via a RAID card, but set to passthrough (i.e., no RAID functionaility).