Alpha_Waffle

My "next" point was addressing the Y:C:F price ratios, which would influence the optimal configuration choices if one knows in advance on which length of routes the planes will be used. IIRC these ratios change with distance (as they should - the utility of a bigger seat is greater over longer distances). It's not something I've ever paid close attention to, however.

Interesting. I'll look into it.

I lied. Price per mile is more complicated than that, and appears to be some collection of linear functions. I'm running an experiment now.

Next topic would be ratio of prices across distances, and the profit-maximizing ideal for those distances.

Already done. The "real-world demand" feature severely skews ticket prices, but for all other routes not included in the real-world update the price is $0.28/mile.

Because it is easily outclassed by both the A300-600 and A300-600R. 22% lower capacity, at best 1 knot faster, with only a 9.5% fuel savings and 17% range increase for the most efficient model of A313 vs the most efficient A300-600R. Sure, it's 25% cheaper, but it's a net loss -- a significant one, at that. 

Let's run some numbers here:

The best A310-300 engine is the CF6-80C2A2 in terms of range and fuel burn. With a 55 minute turn time, you can make 6.21 max range round-trips per week for a total weekly ASM of 9,704,636.811. 

The best A300-600R engine is the PW4158. With a 65 minute turn time, you can make 7.12 max range round-trips per week for a total weekly ASM of 12,209,836.42.

In total, the A313 will spend 128.61 hours in the air during an ideal week, so at a cost of $0.27 per unit of fuel we have expenses of $1,177,793.87 

The A306R on the other hand will spend 124.58 hours in the air during an ideal week, with fuel expenses of $1,260,251.10 

This gives the A313 a cost per weekly ASM of $0.121.

The A306R has a cost per weekly ASM of $0.103.

Let's account for the higher price of the A306R by assuming the aircraft is leased and adding maintenance costs. With a monthly lease of $1,333,333 for the A306 and $995,111 for the A313, and with 0 year maintenance costs being 0.3% of the retail price, we obtain the following adjusted CWASM:

A313: $0.1593

A306: $0.1437

This makes the A306 at most 10.9% more profitable than the A313. This will come down slightly due to landing fees being higher for higher-capacity aircraft.

Note as well that with a 28.9% capacity increase, the A300-600R will require 22.4% fewer slots than the A310-300.

In fact, all of the following are, in general, better options (for the same time period):

747-300

A300-600

757-200

Il-86

747-100