Key issue is what the offset is. From the numbering I would imagine is is 30. I'm afraid the only real way to tell what is going to work is to get a tyre dealer to fit some scrap tyres of the propsed sizes and try them on the car. 6J should be happy within the range 195 to 225. It is unusual to find a rear arch that will take more than a 205 with the exact correct offset though. I think I'd start by trying them with 195/75's (profile reduction is to keep the overall diameter the same). The pinch points in the rear arch are between the tyre and the base unit (not the wing) at the front bottom corner behind the D post and at the rear of the tyre between the tyre and the top link. If this looks nice and clear, you might get away with 205/70, but these are slightly under diameter.
Chris