I might choose the HO version over the HF, although the specs listed give them both the same sensitivity rating: 87dB with 1W at 1 meter, 90dB with 2.83V (2W) at 1 meter, on-axis. Of course, they're both 4-ohm units. I would compare these with the sensitivity of the horn I would be using them with--I bet the horn is more sensitive, i.e. louder, by a good margin, which means you may need to amplify them separately, turning the sub's amplifier up and the horn's amplifier down relative to each other. Whether this can give you the total SPL you need in your application, though, I cannot tell you from the given information.
Just think "87dBSPL at 1 meter," and every time you double that distance, i.e. at 2 meters, you lose 6.02dB and you now have 81dBSPL. Or, every time you multiply the distance from the speaker by 10, you lose 20dB, or at 10 meters you have 67dBSPL.
Also, you'll doubtless be driving this speaker with more than 1W of power. (4 ohms speaker impedance eats up a lot of power, unfortunately.) Whenever you double the power to a speaker you gain 3dB, or a perceptible increase in loudness. Not much, I'm afraid. Multiplying the driving power by 10 times gives you an increase of 10dB, so 100 times (10 to the 2nd power) as much power, or 100W, to this speaker gives you 20dB more loudness, or 107dBSPL in this case. (I don't think they specified the frequency at which they ran these tests. Sensitivity does vary with frequency.)
100W power will give you 107dBSPL from this speaker at 1 meter. 10 meters away, or about 33 feet away, you lose 20 dB. Driving the speaker with 100W gets you those 20dB back, so you have 87dBSPL 33 feet away with 100W. With 120W, as this speaker is rated, you have about 87.8dBSPL, about 0.8dB more than 100W.
The bottom line is that if this speaker can handle only 120W continuously, even pushing it to 180W max., then unless you have a very small room in mind, it is NOT designed for/capable of sound reinforcement work, and likely CANNOT keep up with the horn you have in mind.