OK, using your method, Gonzo, I've just done a KSC - Ascension flight in 21 minutes and 36 seconds. I probably could have shaved off an extra minute if I hadn't overshot the island and came back around. Also my final approach was much slower than yours.
I'm determined to get under 20 minutes!
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Right. Just done a flight in 20 minutes and ONE second. 20:01 on the MET. Annoying, but I'm happy none-the-less.
The issue seems to be the trade off between fuel, speed and time. Much faster than 11.5km/s at ~72 means I have burned into my de-orbit fuel and I'm going faster; so the inability to slow down to re-enter is exponentially more apparent.
Unless of course I perform the pitch around and decel burn earlier, but then that's less time spent in cruise, which even though is faster than 11.5 (around 11.8km/s), means re-entry takes longer. So the net effect is a longer flight.
11.5km/s, with only the default fuel tanks seems to be right on the money. I can't right now think of any way to get it faster.