Here's some further information that may assist in the decision.
Gen 1 "2011-2014" Intake Manifold
Runner length: 12.178 in
Total intake volume: 569.034 ci
Gen 3 "2018" Intake Manifold
Runner length: 16.141 in
Total intake volume: 665.158 ci
Illustration to show how the runner length is packaged into the intake and how the plenum sits in the valley:
FR3E: 2015-2017
JR3E: 2018+
GR3E: GT350
Boss 302 Intake
Runner volume: 29.690 ci
Runner length: 9.327 in
Tuned for 7,750 resonance peak
"The Cobra Jet used the same runner design as the Boss, with the exception being the reduced bump around the injector pocket," says David Born (Ford Performance Parts Engineer). "The Cobra Jet uses a different manufacturing process which allowed the bump to be reduced, which in turn reduces the flow losses around the bump and provides an increase in performance." The Cobra Jet is really just the Boss manifold with a dual-bore inlet added and the strut tower brace recess removed, with the aforementioned having a negligible impact on performance.
Intakes basically have a couple points in which they reach resonance peaks where they best perform. Ford has to tune each intake with their software to meet the demands of each particular engine. The Gen 1 Coyote falls off between 6500-6800, well, because that's where the redline is. The demands of a Roadrunner engine with a 7,500 rpm limit and a GT350 with a 8,200 RPM limit will have (sometimes vastly) different considerations in their design and runner length. You can see that here very clearly in a comparison between the 2018 intake manifold and the Cobra Jet:
The 2018 manifold is hitting peaks at 4,800 rpm, 5,700 rpm, and 7,000 rpm in this example.
The CJ manifold is hitting peaks at 5,400 rpm, 6,500 rpm, and 7,800 rpm in this example.
Now that you've seen a drastic comparison, here is a more subtle one, the difference between the GT350 Intake and the 2018 that was later derived from it:
You can see that the GT350 resonance peaks have been shifted to the right on the graph, to lend in the greater RPM limit of that engine (8,200 RPM limit versus 7,500 on 2018+). The Boss intake has a resonance peak at 7,750 rpm (very similar to the CJ, naturally, as they're cousins).
My newbie opinion is, unless you're doing supporting mods for RPM, I'd probably stick with the stock intake or the 2018 intake. The stock intake should be suitable for autocross, since traditionally cone courses see drastically varying RPM load and not usually staying at max RPM for long distances (at least not at my ability and at the tight courses I attended). The 2018 intake might be a decent choice if you wanted a less expensive road course modification, since it does 'free up' the top end when compared to the Gen 1 intake manifold and lend to an environment where you have a higher chance of running out each gear to the top (but keeping stock RPM limit and not being able to utilize the Boss or CJs resonance peaks out to 7,800 rpm). Let me know if I got anything wrong, but this represents my current understanding.
- Information snippets and graphics from Hot Rod
VMP did a few videos testing many of the intakes available for the Coyote. Here is their Gen 1 video that may also provide some useful insight: