50hz deep enough?

It's really a question only you can answer. I will say your old speakers are not +-3db at 34hz, they are -3db. Having said that, there is no doubt you will sacrifice some bass going to a small speaker. One thing you will discover though, after adjusting, is that the bass you do get is tighter, faster, truer to the music. This is true of any good speaker, so you will get quality over quantity.

How big is your room? If you have the best speakers in the world in a walk-in closet, they won't give you deep bass. The room is not big enough for large wavlengths. A thirty hertz tone is huge....physically. High frequencies are tiny waves, which is why they can't get around cabinets or obstructions. In short, if you are in a small apartment it won't matter as much.

Finally, you can always add a sub for metal or movies. It won't be as accurate, but it will satisfy.

If your current speakers are Paradigm Reference Studio 40s, they aren't anywhere near flat to 50 Hz. Tom Nousaine measured them for Sound & Vision several months back, and if my recollection is accurate, found that they started rolling off somewhere around 70 or 80 Hz.

Given that they provide you with, in your words, LOTS of bass, I don't think you have to worry about other bookshelf models falling short.

(Also, you shouldn't take this as a slam at Paradigm. All speaker manufacturers exaggerate bass performance. And the 40 is an excellent bookshelf speaker.)

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.