I really like the Wee Duper Zilch for an .09!
Follow Jim's suggestions if you are doing to design, shrink another plane. Around 300 sq. in. is what many, today, are using for .15 size planes. Pat Johnston's Ringmaster 307 is a great .15 size modern design that *looks* like a OTS lane. Pat designed the Ringmaster 207 for me to use a Norvel Big Mig .061 on. So, I am guessing about 225-250 squares for the Enya .09. It was a pretty stout .09 for the day.
I'd still go with the Wee Duper Zilch, though! LOL!! It is one of the prettiest Zilches, IMHO.
Big Bear