So it would be faster and more efficient when sticking to the new subset and Nx slower then using the emulation path.

So this is kind of a useless question, because in such a timespan anything can happen. 20 years ago computers had somewhere around 512MB of RAM and a single core and had a CRT on desk.

Now apply that to weapons systems in conflict against an enemy that DOES have modern production that you (no longer) have... it's a recipe for disaster/enslavement/death.

China, though largely hamstrung, is already well ahead of your hypothetical 2005 tech breakpoint.

Beyond all this, it's not even a matter of just slower, it's a matter of even practical... You couldn't viably create a lot of websites that actually exist on 2005 era technology. The performance memory overhead just weren't there yet. Not that a lot of things weren't possible... I remember Windows 2000 pretty fondly, and you could do a LOT if you had 4-8x what most people were buying in RAM.