I think the name says it all.
Pick your favorite historic(al) mission and re-create it as closely as you can in as-stock-as-possible KSP (you can use mods, in other words, just no hyperedit or f12 cheatiness) - from any era (Wright Brothers, anyone?)
As an example, here's my X-15 re-creation, weight is spot on, which made me happy. It wanted to go higher than the "normal" historic 80km so I had to fight that a bit, but I was pleased with the results.
Oh, and Gen. White's record? That's almost twice the speed of an SR-71. In 1962. It's also not the fastest - my bad - that was William Knight in 1967 at 7,273 kph. Knight "holds the world's speed record for flight in a winged, powered aircraft."
Imgur albums or vids are very welcome.
This was in KSP 1.1 beta 64-bit. Your Mileage May Vary.