There are umpteen threads on what NZ Premium Economy is like, but in essence for LAX-LHR (which is currently operated by 747-400):

- 4-6 inches more legroom (38-40" pitch compared to 32-34" in economy). In other words seat pitch akin or better than UA in domestic First on an A320;
- About double the recline of economy, again similar to UA domestic First or slightly less;
- Slightly wider seats (less than an inch wider).
- Business Premier food and drinks service, which will rival UA International First Class in quality. Get far more personalised on board service.
- Less crowded cabins. 3-2 configuration on upper deck (obviously the 2 is preferable) with side luggage bins, or small 2 only side cabins downstairs (which are typically feel more exclusive). In other words, you'll board and disembark before economy class and have far less passengers sharing bathrooms etc. You also share business class bathrooms.
- Priority check in, priority baggage and higher baggage allowance. Noise cancelling headphones with the on demand inflight entertainment.

This IS a superior product to UA Economy Plus, which is just about legroom.

It is an overnight flight LAX-LHR, which may influence your choice. However, use the seatguru.com or seatexpert.com websites to look at the configuration. The seats are wider, deeper reclining versions of the Recaro seats in economy class with significantly more legroom, but all of that space does make a difference.

I never fly economy class longhaul, and have used NZ PE on LHR-LAX a few times. For me it means arriving not feeling like I've been confined like a sardine, not having to push past loads of people to spend ages queuing for a bathroom, and the food is at least edible, at best quite delicious.

Like the previous poster, it comes down to fare difference. Decide whether all of the above is worth it for you for the cost of the extra fare.