I had a 1000 and found it was a little small so I bought a 2000 flask. Got them because you could boil in them then toss in an ice bath to cool. Then I read that repeatedly doing that can stress the glass and some day it will shatter.
So much for the flasks. Now I'm back to boiling the extract in a sauce pan or kettle and chilling then pouring into whatever fits the size starter. Sometimes its a wine carafe, sometimes a five gallon carboy.