Yea - give the Martin Logan Depth I a try - designed to match the speed of Electrostatics.
I have one myself for my very fast mains (they are not horns but have tricks done like lining with 1/4 copper to decrease resonance and increase speed) and their speed is fine. The only issue is, as with any subwoofer, integrating it into the mains seamlessly. I personally only ever use it for HT because the music I listen to doesn't have much low bass. But when I do engage it for music, while I generally prefer it engaged, you can detect some anomalies caused by the fact its not seamlessly integrated - its speed however is fine.
Thank