How much extract would you guys recommend for a 5 gal batch?
I don't have my notes handy from that batch (would be different for a different base beer anyway), but I recommend pouring a liter (exactly) of base beer, then add extract with a medicine dropper, say 0.4 mL at a time, until you like what you taste. Then figure out what you'd need proportionally for a 5-gal. batch, and add half that to the keg. You can always add more to taste, buy you can't subtract.
Also, I find what tastes great in a couple of sips can be too much to drink a whole pint of. You're going for harmony.