50hz deep enough?

Just noticed your post about room sizes. Well, that explains why a bookshelf speaker is giving you lots of bass! Once you move into the larger room, you won't get nearly as much, with that or any other bookshelf speaker.

I have a very elaborate subwoofer system that measures flat to 20 Hz...but...my Magneplanar MG1.6 speakers, when run full range, roll off at 40+ Hz, however they do seem to have very satisfactory bass for about 95 percent of the music. I believe the reason why Maggies limited LF extension sounds OK is because the response is very smooth: uniform without peaks. (They are planar speakers, so there is no enclosure resonance to cope with). Smoothness of LF response is a spec that is hard to define, and usually not mentioned. My advice is to listen to some speakers, without looking at their claimed LF response.

It depends on the speaker, the amplifier, the cables, the room and the stands. I auditioned a set of Linn Katan speakers which the manufacturer insists has a frequency range of 75hz to 20khz +-3db. I heard bass that was WAY BELOW 75 hz in a small room. These speakers has enough bass for me, and I like bass - at least down to the lowest note of a bass guitar or string bass. The B&W Nautilus 805 is rated from 56hz and does not seem to produce any usable bass below that value. This speaker does not have enough bass for me without a subwoofer. Very good, rigid and heavy stands can make a difference in the quality of the bass produced by "bookshelf" speakers.

Pick a few songs with bass parts that you like to listen to and try to audition the speakers you are considering. If you can, arrange for an audition in your home with the speakers you think will work best. If you are buying used on Audiogon, try what you think would be best and affordable form other's comments and your own experience. If they don't work, you can probably sell them for near the price that you bought them for and try a different pair.

I agree with Key metric on the stands. Will make (if they are quality stands) a significant difference in bass quality. Book shelves are no place for speakers. I don't care what they call 'em.

One rule I try to keep for upgrades is to not lose something to gain something else.

The rate of drop is just as important as the cutoff point. Ported speakers usually drop off much faster than sealed speakers. A ported speaker rated -3dB at 50 Hz would be down -12dB at 37 Hz, but a sealed speaker rated for 50 Hz would only be down 9 dB at 37 Hz.

If you put speakers near a wall or (especially) corners, you will get more bass, prob'ly at the expense of other things like imaging and soundstage.

I disagree with Hammy's assertion that big waves can't fit in a small room. I've heard this often. If this were true, car stereos would not be able to play below about 120 Hz. If you've ever sat in an IASCA car, you know car stereos can reach subterranean levels of bass. You can get bad reinforcements and cancellations that will make it difficult to get good even bass. Car folks use various forms of equalization to overcome this (some to very good results), but this is rare in homje stuff. If you're not sure of your room acoustics, it may be better to stay away from very deep bass, but with enough patience, money or luck, it can be done.