I have had a little experience in a Stellar SEL, so I’ll offer the following …
The very first ski I paddled (2011-06-30) was a stellar SEL. Previous to this test paddle, I had the seat in my Necky Looksha II raised about 3 inches (7.6 cm) above normal seat height (it was a tight fit) for about a month of paddling. This really helped me progress into a performance ski very quickly. Anyway, I paddled the SEL for about 30 minutes in smooth water that was somewhat shallow (5-10 ft, 1.5-3 m deep) and not much breeze. Immediately after taking a couple strokes the first time in the ski, I was off chasing the nearest power boat to attempt surfing wakes. The Looksha II has very nice manners in chop and short-period waves such as powerboat wakes and steers in a very neutral manner. The SEL was more akin to negative yaw stability in the wakes. It always wanted to broach toward the origin of the wake. The SEL had a smallish, trapezoidal rudder, so this may have a lot to do with the handling characteristics. Yes, I was doing all the typical body English to help correct the ski in these situations, but to little avail.
The SEL had tons of "secondary" stability. Even for a complete newbie skier (with high-seat, low-stability experience). However, I was swimming in the bucket (the bucket is enormous). At the time, I was 215 lbs (98 kg), 5'-11" tall (181 cm) with a speed-skater’s arse (good sized, wide, muscular legs and butt due to much speed-skating and training). I did not feel secure in the cockpit, though at the time I liked the 3-point brace even though the adjustments are kinda agricultural with those wingnuts. No creaking here.
Coming from the Looksha II (20 ft x 20 inches, 6.1m x 50.8 cm), the SEL was very fast, and about as stable as the looksha with raised seat.
Another attribute I do not like about the SEL (after paddling my new V12 Ultra since 2011-07-15) is the double foot straps. You just cannot get your feet close enough together with double straps and the centerline rail of the 3-point attachment system. I appreciate the lack of stuff in the way on the Epic foot boards so that the feet can be very close to the centerline of the boat, enabling the paddler to truly pump on the board without disturbing the boat's balance as much. Especially in the very windy, rough, choppy, multidirectional stuff I paddle in much of the time. I try to rotate as much as possible using lots of leg drive (push and pull) as well as torso rotation, but with the feet to the outsides of the board, any ski will have stability issues when pumped hard. The point I'm attempting to make is that a wide footboard and well is certainly not what a performance ski needs... a narrow catch would be far more advantageous than more volume. Yet another point a really did not like about the SEL was the wide catch. Even though the SEL was supposedly nearly 3 inches (7.6 cm) narrower than my Looksha II, I kept on hitting the sides. Perhaps this for I felt as if I was sliding side to side in the seat.
Comparing this to the E-V12-U, the foot well is nice and narrow (I have U.S. size 12.5 feet, DD wide) and I still have more than enough room on the board (wish it was narrower), the catch is quite narrow (for a ski), and the bucket fits me perfectly. At first, the bucket felt perhaps a tad narrow, but somehow my arse adjusted to it and now it feels like home, and I can pivot my hips to a large rotation angle while feeling very secure in the bumps. Perhaps a good fraction of the V12’s fine manners in the bumps is the control afforded by the excellent fitting (for me) cockpit.
The one of the very few attributes that irks me about the V12 is the creaking foot board. This is easily remedied by some electrical tape on the bottom edge of the board. No more creaking. And nothing in the way of my heels like there is in the Stellars. I believe the boys (Greg, Oscar, et al) at Epic have enormous amounts of experience with olympic and otherwise high performace paddling, and they came up with a fine compromise between foot board rigidity and proper foot placement.
To clarify, I believe a wide foot board is not advantageous if one is trying for the most effective paddling form. Bla,bla,bla.