Have flown KAL hundreds of times, most their fleet types and classes, including the new 747-8i. Fact is 1st class cabin has not been improved as much as business has, still a very fine experience but just a few inches wider seat, you won't feel that difference much, slightly bigger screen and exactly the same menu! but nicer silverware.

1st class Kosmo suites' "walls' are so low, when you are seated upright you can see the cabin, however the 747-8i business class is brand new and one of the very best in the industry; fully walled all around, if you seat next to the window all you can see is the window, your screen and walls, almost absolute privacy, the only person you'll see is your flight attendant, lays fully flat, very comfortable, not worth the extra miles for first class where you are not getting much more. In the 777 however you still have the older version of the prestige sleeper seat, still lays flat, a very short privacy screen and a cumbersome hop over your neighbor to go to the washrooms in mid-flight if you are flying window seat. Hence my recommendation, use 1st in the 777 (the Kosmo suite here does not close completely but is a large comfy pod), and you'll be more than happy in business in the 747-8i.