I looked at the sim and it is quite close below 80Hz.
This one should have less efficiency and less output above 40Hz on paper. It should have a bit more output near tuning. I'd say the original sims as being the slightly bit louder cab overall for music apps or live sound (kick drum, percussion fundamentals, most of the content being above 40Hz etc.).
I've found over the years I like smoother responding wider bandwidth systems vs systems optimized for more sensitivity over a narrower band of operation. This is part of the reason I decided not to do a straight slot. I wanted extra upper bass output and extension well beyond 100Hz as part of the design goal. Often times you'll see guys using subs for 30-70Hz and another set of kick bins for 70-140Hz or whatever. Usually due to sub bins with degraded upper range behavior or just not enough output. I'm not a fan of that approach. I'd much rather have one cab that can handle everything. I think the sim you proposed would be fine. I tried to get the top end as extended as possible on this one.
Another reason I didn't choose a large straight slot was to more fully enclose the drivers inside the cab. Most of the time I notice non harmonic mechanical and operational noises before HD gets to be offensive. The acoustic roll off of the slot above 100Hz should help lower HD a bit, but with the driver cone edge only 10" from the end of a large slot with line of sight to the outside world I'd expect there to be more operational noise leakage, though HR doesn't show too much of a difference. I'd like to see that tested actually. Also the drivers would be a little more susceptible to rain or a drink spill, but either arrangement is safer than a direct radiator cab!
I didn't go with a push pull driver arrangement due to the minimum clearances needed for the drivers (10.5" driver depth + a large dustcap and +40mm excursion worst case scenario minus some for the baffle thicknesses and depth to the dustcap below the frame plane) and the fact that most high excursion sub drivers make quite a racket from the motor and suspension when pushed hard. Even more of a reason was the uneven loading it would present on the drivers. It would be much more involved and difficult to design the cab to evenly load the drivers with one inverted. Not impossible but it would complicate things. I'd give a rough guess that there would be about a 25-30L difference in the vented air volumes seen by the drivers. Tuning would be slightly different unless compensated for and the throat area would be a concern. I know this has been done in plenty of cabs before but I don't know if I trust it with the kinds of pressures that can be developed inside something like these. I didn't think the potential lowered even order distortion outweighed the concerns with uneven loading and possible mechanical noise from the inverted driver motor. The forces inside these can be pretty ridiculous.
The force cancelling works really well on it. It's not like the drivers are 90deg rotated from each other or even 45deg. It's only a 12deg offset and it's a 250+ lb sub. In use the cab has no perceptible rocking from the driver operation. That small amount of offset from exact opposition plus the sheer size and mass just doesn't add up to any real rocking forces fore and aft. Technically I'd guess a perfect driver opposition would measure a bit lower with an accelerometer but in practice it worked like expected and it's a complete non issue. Regular old panel vibration and bracing is a much bigger concern. The Skhorn has been quite good as far as that is concerned when compared with most other large cabs, but this is always a battle on big subs with tons of output.
About Edge and directivity. Keep in mind that the math is simplified and goes back to the point source mic placement method. If the radiating points are spread on one sub and focused on another you can never truly get the same mic distance from the two. In practice there is a very large area that one is trying to cover usually inside of a room with boundaries. It's complicated. One sub is more diffuse but that's not necessarily always a bad thing. Edge is a good tool but I don't get too caught up in an apparent half dB advantage here or there. Most of that directivity happens above 80Hz unless the baffle area starts getting truly large.
One way I like to think about this is with 2 different philosophies. The first would be maximize the baffle area for the cabinet (think DTS-10 shape or similar) and get as much out in front of the cab with the drivers and design as possible. However at what point does this become impractical? Let's say the cab has a 60x60" baffle and is very shallow and gets some extra forward gain over a very similar design with the same driver which has a baffle of 30x30" but is much deeper. At some point you run into limitations in available depth to use and/or available baffle area. How many 60x60" baffle cabs are going to be able to be arranged? In a lot of cases not too many and eventually you just need more cabs and drivers. You could fit 4 of the 30x30 subs into the same baffle area as the 60x60 that would outperform it. The best case as far as potential output density per baffle area goes is that one entire face of the sub is radiating surface area. That's not going to be the best for directivity control though. You also end up with deeper cabs to get your cab volume. Tradeoffs.
Vent area is vent area I'll give you that as an advantage for sure. This is the #1 priority I would have when redesigning the Skhorn. Mostly to work better with the lowered tunings. I try to avoid turns in vents when possible though. The reduced area of the slot for the drivers would increase air velocity over the horn expansion type though. I have some new thoughts on designing vented subs that I haven't gone to far with yet but I'll share once I think it through a bit more.
Anyway that's part of the thinking behind not doing the straight slot or push pull drivers originally. It all comes down to tradeoffs and design choices. None of it is black and white it's all grey area and what makes sense for each case.