If you're looking at flying in C, I'd agree with oz that it's not worth it unless you get the "747". In First, however, any of the aircraft would be fine, bearing in mind that you're paying for the novelty of the experience, for the service and food and pampering and sense of occasion, all of which are unaffected. The smaller (but still extremely spacious) seat pitch and lack of PTVs are not really an issue on a 2.5 - 3 hour flight with your partner, when you can be sharing a bottle of Dom and getting some quality time instead.

IMHO, at those prices 'F' is worth it for the novelty and the experience, whereas 'C' probably won't be special enough to justify the expense. Although, if you're an AirPoints member, the extra status credits could be useful.

Let us know what you decide to do!