This is just a question because I don't really understand why the Spit 8 is at 10 ENY when the Spit 9 is at 20?
Mostly engine power. The VIII is faster and climbs better. It also carries more fuel. There's very little difference between the VIII and XVI other than roll rate but that is a HUGE difference between them particularly at faster speeds. The VIII is also saddled with the .303's rather than the more effective .50's that the XVI carries.That said, I think the IX is a better aircraft than the VIII. It's silky smooth handling makes up for all of it's deficits to it's bigger brother.