Aerogant,
I too have been very impressed with Earthstar's planes, since I first saw one at the EAA Arlington, WA airshow a couple decades ago. Their fully cantilevered wing is stiff and strong... the best and most efficient design in the U/L industry. I've heard it called "the hardest working wing in the industry."
Titan aircraft copied or bought the wing design, and is using it on their planes. And I heard some other company recently copied it. People who have flown the planes are extremely impressed with their crisp handling. And they require less engine horsepower because of the lack of struts and their aerodynamic efficiency.
I even used some of that thinking in my designs... make an efficient airframe that only needs a small engine to perform well. For legal Part 103 U/Ls, that means putting more of the weight limit into the airframe, and less in the engine. That leads to crisp handling, strong airframes. Doing the oposite, leads to floppy winged designs.
As far as the stall speed... a fully sheeted (on the upper surface) wing, that has a good airfoil will have a significantly lower stall speed than one that isn't. I've seen STOL wing tips on some Earthstar planes. That helps a shorter wing pass the legal stall speed limit. And shorter wings have a better roll rate, giving a very sporty feel.
Every aircraft design is a compromise. Most U/L pilots want a lot of fun for their dollar. So many U/L designers find the cheapest, easiest way to make an aircraft that is safe to fly. For a legal U/L, most everything has to be compromised for weight. Many want the reliability of a Rotax twin. So everything else on the plane needs to be minimized/compromized to make the weight limit.
I've seen airfoils that are severely compromised, usually to save weight and/or expense. A few common compromises I've seen: No leading edge sheeting (very common); an airfoil that is completely flat on the aft half (for example Kolb); an airfoil with an extra bulge for the rear spar (for example MiniMax).
It's really hard to make a fabric covered wing that has a perfect airfoil. The fabric dips between the ribs. Designers can make the leading edge sheeting come back farther to minimize this problem. Then there's the problem of the aft edge of that sheeting, creating a slight corner. We can add more ribs or false (half) ribs. But that adds weight.
Another problem with passing the stall speed limit is in FAR Advisory Circular 103-7. The wing area prescribed in that Circular is based on the poorly carried out, fabric wings that were common when it was written. It does allow less area, if you officially demonstrate and document the actual stall speed.
A manufacturer, like Earthstar, can go through that procedure, and pass out copies of the document to their customers. For the rest of us, it is often easier to just use the formula in the Circular, and have extra wing area, and the resulting extra low stall speed.
I have made efficient enough wings that stall slower than the Circular's formula suggests. For example, an under-cambered wing has a similar effect as having flaps down, as far as stall speed. The Circular doesn't make the distinction.
Remember that we have to be able to prove that our plane is legal. The FAA doesn't have to prove that it isn't. And usually the FAA won't question your plane's legality until after you crash. So there's no way to demonstrate its stall speed after the fact. Either you have the required documentation on file, or you'd better have the wing area in the Circular.
Looking on the positive side, the extra wing area tends to make the plane climb and glide real well. But on the negative side, the extra long wing tends to have a dismal roll rate. My next U/L wing will be fully sheeted. I ordered the materials for it and will start construction as soon as they arrive. I'm trying progressive spoilerons with this design to try to get a decent roll rate. It will have the extra wing area as prescribed in the Circular.