Best Efficient versatile Speaker reaching 30Hz?

I believe Soliloquy 6.3i and 6.5is would both fit the bill and not break the bank. Unfortunately I don't know the status of the company, but there are usually a few used ones at reasonable prices. I have their 5.3's that don't quite make your cut, but are outstanding speakers by any account and offer great bang for the buck. Underwood Wally sells them new and B-stock at reasonable prices and is an excellent dealer.

BTW, I don't think I'd agree that "efficiency is the key" when it comes to speakers. Perhaps you are not stating this well. I've certainly heard ineficcient speakers that sounded great, and efficient speakers that sounded bad within specific respective systems. I think "synergy" would be a better word. With that in mind it may be good to be more specific about what you'd be pairing these off with and what exactly are you after that you don't have now.

Marco

Klipsch K-horn is quite possibly the loudest speaker on earth

I do like the K-horns when paired off with the right amp, and at 104db they are mighty efficient. They will not, however reach down much below 30hz in my experience. Tight bass is not their forte, though of the range of the older Klipsch Heritage line they do Bass the best of the bunch given the corners they were designed to be positioned in. Their specs indicate 33hz at the bottom. Fast dynamic midrange, crystaline clear, and yes, loud as you can take if that's your poison. If you are hooked on sub-30hz bass you will need a sub with K-horns (or any of the Klipsch Heritage line for that matter).

Marco