Comparing Military Aircraft

I'm working on a project where I want to compare military hardware between the US and China.  I've thought of a couple of options, including the tonnage and Verticle Launch System capabilities of ships, as well as the range and payload of ballistic missiles.  But what I'd really like to do is trace the evolution of each country's relative aircraft performance over time.

Having fiddled around with a few basic methods, I've come up with a formula to generate an 'aircraft capability score'.  The four elements it incorporates are max speed, max takeoff payload, combat radius, and the aircraft's generation--as a proxy for the level of technological sophistication.  To come up with a number I divide payload by a theoretical 20,000 kg max, combat radius by a 2,000 km max, max speed by mach 3.0, and square a random coefficient (1.5) by the aircraft generation.  

For example, a third generation plane with a 10,000 kg payload and 1,000 km radius and 2.0 mach would have a 5.04 score.

There is certainly no science to this.  I choose the 1.5 generation coefficient simply because 1.1 and 1.2 left me with scores were the F-15E is superior to the F-35 (and it might just be) and a coefficient of 2 diminished the other factors to the point they were virtually non-existant.  I am certainly open to an arguments regarding different and better ways of doing this.