Wrt point 4, most of my driving has been done in/around Surrey/Sussex/Hants borders and suggest the following:
New cars are faster to a point. But...
General traffic speed is quicker, so less overtaking margin, although perspectively so as alot of limits have actually dropped. Even 10 -15 years ago, you could easily be the fastest thing on the road without actually exceeding the limit... now not so, as to overtake slightly faster moving traffic safely you need to be well over the NSL, assuming it hasn't been replaced with a 40/50 limit.
Part of the reason for this slightly higher traffic speed must be due to better braking everything has ABS or ESP as standard (chuck a current car into a tightish bend at 60 and you don't crash and die*) and refinement means cars disconnect the driver from what they're doing... compare a Mk1 Cavalier to the current Astra.
You didn't drive a 1600 Cavalier at the NSL on single carriageway roads (unless you were in a rush or young and fearless) as the it wasn't really comfortable to and the brakes were woeful, whereas the latest cars are quiet, stop on a button, and don't take two days to hit 60.

* Don't try this at home kids. No, really don't...