Another thing to consider is how useful is that 85dB at 10Hz or 65dB at 4Hz ?
From my readings so far, you need at least 100dB @10Hz, preferably 110dB to notice the effect, way way more for 4Hz. If those values in the graph are the max those subs can achieve, you probably will not notice the advantage the sealed shows in the graph.
The advantage that the ported shows
at 20Hz is high enough, and large enough that you would notice that much more.
Now if that sealed sub has the headroom for even way more SPL below 10Hz, or you can afford to stack enough of them to raise that low range in the 100+dB, you may be happier with a sealed setup if low extension is what you are after.
With a single or couple of subs, if it is low frequency you are after, my bets are on ported, tuned between 10Hz-20Hz depending on what you are working with, and what works best for you
EDIT: Lol, just learned 'at' 20HZ is not a good thing to type, apparently there is a member named '20Hz', so it would count as a mention. Wondering how many mentions he has accumulated so far.