This is solely my experience, but I tried to get a transatlantic F flight on LX for my honeymoon (mid-August), and all were snatched up already, from all possible North American gateways. Fortunately, LH was available. However, if you can get LX F it is worth it by all accounts.

I'll second the suggestion of AC biz, as most are now lie-flat and you can save on the miles. You may, however, have to endure additional security clearances depending on the gateway.

The Cranky Flier blog has a review of the NZ LAX-LHR business cabin, whose availability I have heard also disappears quickly.

Finally, I thought OS did not have an F cabin? Is this still true? I like their coach.