I did manage to get all 800 points! Funnily enough, the hardest part wasn't the fighting, but the biplane. I used Virtual PC to save and load the game state during that sequence (since you can't normally save during it).
I think the highest Episode score you can get is 505. Here's how...
-Use Cunning Plan 3 to get past the students (both ways)
-Talk past the Butler
-Give the painting to Guard 4 and get the inner vault open
-Give Mein Kampf to Guard 8 and disable the alarm system
-Get out on the window ledge and enter Henry's room that way
-Talk past all the other guards in Castle Brunwald, then
knock them all out EXCEPT for Guard 2. It's damn hard!
-You need Guard 2 alive for maximum points
-Unlock Henry's door
-Get captured by Guard 2
-Give Vogel the real Grail Diary
-Talk past the checkpoint guard on the road to Berlin
-Get Hitler to sign the travel pass
-Steal the tickets at the airport
-Start the biplane
-Get shot down by the first plane that attacks you
-Talk past all the checkpoint guards except 2 and 6
-Bribe guards 2 and 6 (you should have enough money if you knocked out all the Brunwald guards)
-Pick up the Grail before Elsa gets it and give it to the Knight