Kevin,
Can you clarify you first comment as you reference the E6 twice. Is the E6 designed for lower wind speeds than the E5 or the other way round?
Andy
Yes, a typo. The E6 has been optimised for lower hull speeds than the E5. That said, it is important to realise that the main factors influencing the drag of a hull are its length, weight, waterline beam. There's not a lot you can do with these in the Cherub, so the performance differences between the E5 and E6 are likely to be small. Crew weight, for example, would have a much bigger impact than the differences in hull shapes - a lightweight crew in an E5 would still outperform a heavier crew in an E6 in light winds. Rig set up, sail trim and sailing skills are, as ever, of paramount importance.
Design is all about compromise - if you improve one area of performance, you'll almost certainly degrade another.
Hope this helps.