Data from Boeing Website here
Boeing might market the aircraft that way, but as Going Boeing said a premium carrier wouldn't cram that many seats in, especially on ultra long haul routes.
CX is taking delivery of the first of its 777-300ERs later this year. I understand they'll be fitted out with around 300 seats in a 3-class config. I imagine a 3-class 777-200LR in a similar config (ie flat beds in F and J class) would only have around 250-270 seats.