I've heard once that OK itself comes from the Greek words Ola Kala (=All Good). Especially if this is true, you can say Ὅλα Καλά, but in any case the meaning is the same. By the way, perhaps we should stop using this thread (on pronunciation) to talk about everything! Just open a new thread. :)
I am actually quite fascinated by the accents of Greek, since my undergraduate degree is in music and I lived in China for nine years afterwards where tones are extremely important. From my various study and self-study of Greek I know that the genative always takes a circumflex accent, which may have a corresponding similary to the Chinese third tone except in a reverse way. But I realize most Westerners cannot bear the though of three Greek tones and are happy to be rid of them at the earliest opportunity. I just wish I could have seen a Greek tragedy on some ancient stage to find out how the music (in twelve modes, only two of which are used today in the West and a little more in Gregorian chant) sounded.
Please note that the genitive does not always take a circumflex accent - not in singular number words having their accent in the last syllable (think e.g. of the word "man" = ἀνήρ, gen. ἀνδρός). Only in the genitive of the plural number, if the accent goes to the last syllable, we have always a circumflex.
I'm very glad that I've found Elpenor; the website is unique and full of important texts, and the forum promises useful discussion. And it is a best playground for us to exchange and learn experience. That is the reason why I'm here. I wish to receive helps from all members of the forum. Thanks in advance!