Gosh, a good old fashioned thread Necromancer!
I believe the main two pillars of aircraft designing are
- Range and
- Capacity
Every decision is taken to satisfy these two criteria correlated to financing and practicality of physics.
When I used to teach this stuff, we were left to our own devices how (universities are great like that), I actually decided we had four pillars
- Role
- Operating environment
- Available technology
- The regulations
Range and capacity will sort of sit between role and environment. Your discussion about the alternate benefits/disbenefits of different engine types and wing configurations pretty much falls into "available technology".
I absolutely agree that swept wings give better transonic performance by modifying Mcrit, but disagree that a low wing improves high speed performance particularly. It's more I suspect a case of since the length of the fuselage necessitates a long undercarriage, a high wing would put the engines too far off the ground.
G