JJJ, I have an idea for how the ME might improve performance. I'm quite certain that WOFF performance temporarily suffers whenever either allied or entente flights take to the air during the player's mission. Furthermore, I think we all know that overall performance goes down as the total number of AI flights goes up. I suspect that a large number of the AI missions that are taking place will never even cross paths with the player's own flight, unless of course the player (or the AI) decides to deviate significantly from the predetermined mission flightpath.
So here's the idea: could you implement an option to "delete" AI missions that ME calculates as "unlikely" to cross paths with the player's flight? This would help to improve performance (albeit at a slight cost to historical realism), especially in late 1917 and into 1918.