Ancient Greek GCSE?Watch
I don't know what the new greek 9-1 exam will include, but if they continue with set texts, which they probably will, it basically means you have to memorise the translation of a really long greek verse writing (which is like some old greek poem by some famous greek guy) and another translation of a greek prose writing (which is like normal non-poem literature from some famous greek guy), and be able to recognise the greek words in their original texts. That is like the greek 'literature' part of things; imagine english literature and all that analysis you had to do for english, but now you do it in another language (alliteration, metaphors, etc). The greek 'language' side of the course would just include you memorising a list of words which OCR give you, and also learning grammar like modern languages, although the grammar is a bit harder with greek imo, literally just because it isn't an english alphabet so its harder to remember what goes where. Sorry for the muddled explanation, but if you need any further clarification, just ask.
So overall it just depends how much you hate languages, and whether your desire to do 1 more gcse is greater!
Don't put your other subjects at risk of being lower by over stretching yourself. Whatever you choose, make sure its what you really want to do