For a lot of 77W operators the only way to get a decent value on their older aircraft is to convert, as the passenger valuations are quite low these days. .
There is also little in the way of alternative at all. Every single cargo aircraft you can buy new is the same or older generation the 77W is, and the only other P2F conversion on the market is the A330P2F. And if you order that one today, you´ll get it in 2025 since the conversion line is sold out. You might even have your A350F on the tarmac before you get your hands on a A330P2F.
The various generations are as follows:
Latest - both engine and air frame:
A359 and A35X - only passenger - A new build freighter version is being considered but no orders on the books yet.
B788, B789, and B78X - only passenger - no announcements that Boeing is considering a freighter here.
B77X - only passenger but new build freighter is anticipated. I placed here as both new engine, new size, new wing.
Major upgraded- latest gen engines on older air frame:
B737 MAX - basically only passenger, unaware of any orders for a freighter either new or conversion.
A320neo and A321neo - basically only passenger, unaware of any orders for a freighter either new or conversion.
A338neo and A339neo - basically only passenger, unaware of any orders for a freighter either new or conversion.
B748F and B748i - The 748i is only passenger as new build, too small of fleet for major conversion program. The 748F had its last call for orders, 748F sales were less than anticipated - production ending.
A generation back - engine and air frame
B77W - best performance of this group - only passenger currently, several P2F conversion programs going thru certification. Probably hottest conversion prospect.
B77F - best performance of new build freighter but a sunset of the order stream is apparent.
A380 - unlikely to have a conversion program.
A330F - lackluster orders for new build.
A330 P2F - Covid changes economics, now a promising conversion candidate but very few converted so far.
A340 - some conversions I recall, but no significant conversion programs.
A320ceo - conversion programs beginning, not sure how significant.
B737ng - conversion programs in place, conversions occurring with pace building.
Slightly more than a generation back:
B747-400 Passenger - many converted in the past, no new conversions in a decade.
B747-400 F - no new orders (obviously) - nearly entire fleet in service.
B767 freighter - steady order book at this time but a sunset of the order stream is apparent.
B767 P2F - the -300ER models, in particular the GE ones are the most popular conversion feed stock currently. The -200 and non ER -300's have low conversion prospects.
B777 - not 300ER or 200LR - too many different variants and difficulty with converting due to the floor beams. Low conversion prospects.
Several generations back:
B757 - former high demand for conversions, limited feed stock left to convert.
A300, A310 - no new conversions in over a decade, fleet is in the retirement phase.
MD's - no new conversions in over a decade, fleet is in the retirement phase.
B747's before the -400 - fleet is in the retirement phase.
and many other older freighter frames.
I will use a proxy for efficiency and economics, the current orders and activity. Those invested in the performance select the aircraft that will be the most profitable, and drop the least profitable. So trends in utilization tell a lot about the relative economics.
The hot models in the market right now is the 77W P2F conversion, and the 767-300ER conversion. The NB 738ng and A321ceo P2F are both building programs. A building but slower A330 P2F demand.
New build freighter orders have been OK, but not great. The initial cost is too high, reducing the economics to below other choices.
If the economics of the latest generation new build freighters looked good, there would already be a lot of B77xF and A350F orders in place, but not so far. With each upswing in fuel prices the latest new builds improve, with each drop in fuel as well as valuations the older model conversions improve.