I have had a 4.0, 4.5 & 5.0 Force for the last four years plus a 5.4 Boxer (all updated every season) for the reason that they will all fit on a 4m mast with the boxer needing about 16-18 cm of extension.
the boxers have been noticeably improved every year and with the new sail cloth being 30% lighter im looking forward to trying the new ones.
check out the link above from a light wind day on the 5.4 and a OES TF78 on a light wind day.
i reckon they are as good as any other wave sail and why i chose a whole quiver this year !