I know that this driver has as much displacement as a beta 15a, which is a 15" driver, and some people like them quite fine for bass, especially as a B-15 replacement driver, and they both have the same Fs of 35 hz. Their EBP values are relatively close as well, with 62 for the legend and 56 for the Beta. They have similar Qts values, of 0.54 for the legend and 0.58 for the Beta, with Vas of 5.56 cubic feet and 11.82 cubic feet respectively as well. So to get a similar low-end response you'd put the legend into a smaller box because the compliance is smaller AFAIK. As far as the legend goes, its high-end extension goes to about 2.3 khz on their spec sheet, and the Beta goes up to 3.7 khz, and the legend at 94.1 db of sensitivity has more or less 4 db less sensitivity than the beta at 98.2 db. So, in a box designed for similar low-end extension, the legend would go about as loud in the low end as the beta, but would need a bit more than twice the power for the same volume (because twice the power makes, at best, a 3 db increase), but the Beta would probably seem louder or cut through some mixes better even at the same objective volume or SPL because of its greater high-end extension. To put the 2.3 khz upper limit into perspective, the driver in my 115 cabinet is a different legend, and goes up to about 3khz if I can recall, and I would say it's a pretty "classic" tone, with a good bit of low-end focus that doesn't go too high - this driver will be even bassier. If you're okay with a good low-endy tone, that goes to a smooth midrange and not much above that (which with your Gretsch with flats I'd say you're okay with that), then it should be a great tone for you and should at least be loud enough for a dusty garage, and some smaller bars/bigger noisier cafe's. As for ported vs. sealed, you'd be able to just plain get more low-end with ported, but it'd be a bigger (and therefore also heavier) cabinet, and with as little high end as you'd have, you'd probably be making the whole sound a bit muddier with the port extending and backing up the low-end response. The small sealed design has an f3 of 70.3 hz, the small ported has an f3 of 51.6 hz, to put that into perspective, most would say that an f3 of close to 60 hz is great for a 5-string, 80 hz for a 4-string in standard tuning. So even the sealed box would have good extension for you to mess about with drop-d and such.
Okay, that was a big, and long paragraph.
TL;DR - Based on what you've said you like, this driver could be a good fit if you don't like highs, or high mids even, and should be good for at least a garage and probably small venues too, depending on how loud your drummer and guitarist are. If you want more mids/highs, a 5-8" midrange driver shouldn't be too hard to figure out, or you could just grab a beta 15 with the same displacement, more sensitivity, and a bit more mids/highs. As for sealed vs ported, it kinda doesn't matter with this driver, either way should have plenty of pillowy low end.
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