If you ask Samsung, they say yes, of course.
So it's up to you to find an independent opinion:
1. Read the reviews
2. Ask the salesperson in the shop to convince you to spend 700 USD more, by explaining what these features do and demonstrating the effect with a good UHD source. For 700 USD extra revenue for the shop (and probably a bonus for him) he can be expected to do some extra work.
KS900D is featuring Supreme MR 240 and Supreme UHD dimming. Is this a marketing gimmick? Is it worth the extra$$$ to have these features? Samsung has a model KS800D that has UHD and MR 240 but they aren't Supreme. Price for the KS900D is $2,479.99 and the KS800D is $1,799.99.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic