I have both the 7'8" x 30" and a 8' x 31" , After comming off a Paddlesurf Hawaii Ripper 9'6" x 30" the differance is like going from a 10ft longboard to 7' fish , The 8 footer is super easy to paddle, catches mushy waves easily and is very responsive, the beveled rails to hard tail rails make these boards forgiving dropping in yet they have good drive out of bottom turns and carve nice cutbacks rather than the feeling of "floating" the nose around like the ripper and without alot of foot repositioning, the 7'8" is remarkably more agile, weighs 16lbs, Light but not ultra light and has flaws in the glass job as well. it handles shoulder to head high ( about the extent of my ability) steeper waves, is fast down the line and can be leaned on even harder during more aggresive turns. A bit slower to paddle in but tracks better than the 8' probably due to lower volume.
The above is just my opinion/observation, I am not a seasoned pro. I bought these boards because they happened to be availible when I was looking for a short performance board while at a vacation destination and nothing else was outside of ordering and waiting for delivery. I would have liked to compare with other Simmons style boards before buying but it wasnt possible.
I'll be trying the 8' out on some standing waves in Co. soon, I am thinking the beveled rails will make it a decent river surfing SUP.