I froth about 200ml on my Giotto in a small jug. I only use a small amount of that at a time, (for macchiato or small Cap), then re-chill, top up, and re-froth as needed later.(And I can hear sharp intakes of breath from professional baristas as I speak). But its only for me, and seems to work fine.
Not sure frothing 70ml at a time will work on my Giotto though.