Rick, NX2 is slower because you are working on a very large NEF 16 bit file and all the changes you make are being saved back to that file along with the original image. Since the NEF file has all the info off the sensor, you have about four stops to play with and that means the U-Point controls more info. It is slower, but the results are extremely better.
I use Lightroom for proofing changes and NX2 for the final print. Just for the speed when doing a lot of images.
By the way, you can use NX2 on tiff and jpg. It's faster then NEF.
Billy
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Billy Mitchell Photography
San Antonio, Texas
Wedding | Portrait
www.billymitchell.com