^^ Think you've both hit the nail on the head there - the slightly pulled tail / hard edge is certainly needed for confidence in the bigger stuff - and the Bing / Pam's modernised template does the trick (Pam - your first one was based on a Bing if memory serves?)
Also handy to note, that Simmons built his boards wide due to his disability (he had a history of problems with his leg) and needed a wide planing surface - the more successful shapes these days seem to be slightly narrower, more friendly tail etc So originally the width of the thing had little to do with any kind of performance aspect - Simmons used his engineering knowledge to make the hull and the rails the vital ingredients. It's rumoured that he had a sub 5'0 styrofoam version back in the 50's
Interesting your comment on the 'chop' Gav - I picked up mine specifically to ride in chop (and one of our breaks, builds,back's off, doubles up - all sorts - found I had to paddle with my head practically over the nose of the board so it 'digging' in didn't really affect me.
I guess all of these small boards come down to one thing - Rob Lions point of proper foam / volume distribution - usually what you lack in length you make up for in thickness - foam is your friend
BTW, for what it's worth - one of the reasons I found the Simmons not as engaging as i probably would've liked (which no doubt would've been rectified by better waves / more perseverance) is that coming from LB's I do love a single fin - for that reason I'd love to give one of these a gohttp://25.media.tumblr.com/tumblr_mb2kj0HMn51qbfil8o1_1280.jpg
Marc Andreni's stand-up Velo circa '71 - surely that can't be much over 5'6" ?