If you want to shed a few grams, then put that croissant down. No need for Dura Ace, and compared to Sram's older high end cassettes these Ultegra cassettes are much cheaper and quieter. Worth every penny, and when you can find them for around 50 it is even sweeter. Shifts are smooth and quiet.
I use Rival shifters, brakes, and rear derailleur with an Ultegra 12-25 cassette, Ultegra front derailleur, Sram Red 53/39 crankset, and yokozuna cables. Couldn't be more satisfied with the performance of my Frankengruppo drivetrain