50hz deep enough?

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.

for a small room like yours, the model 1's will sound very nice for your musical taste except for 110db headbanging metal. i used to own a pair in my audio room that is only a couple of feet bigger than yours. you can always get a musical sub to compliment the model 1's. Rel and totem make excellent subs that would work. i don't agree with some of the threads above about bookshelf speakers are intended to be used only in smaller rooms. i upgraded from the model 1's to the totem mani 2's. these are a full range bookshelf speaker that sounds great in a small room as well as in a large room (i have a pair in my audio room (12 x 14) and another pair in my family room (16 x 20). the mani 2's are keepers no matter what size of room I will have, i just might have to compliment them with larger amplifiers for a larger room.
good luck!

Nickway: I ignore numbers Key Metric makes a lot of sense. The system synergy that gives you the most pleasure is the one you should buy. Bookshelves are never going to play the lowest most octaves and your room really isn't large enough to sustain the deepest bass. The question is how deep do you want your bass to be. I have had speakers wich are much bigger that supposedly cut off at 50Hz it never troubled me because I wasn't playing pipe organs or earthquakes. Most of the musical bass I look for is easily found above 50Hz plenty of slam just not a lot shudder and vibration boominess. I now have even larger speakers that claim 30Hz which occasionally sound too loose for me. I didn't appreciate the sonics when the really low tones are played. Truly deep bass is by its very nature less tight sounding and not always a good thing musically especially after years of enjoying slightly higher cut offs. I had to switch amps to avoid that wretched sub woofer vibration which can mask the vast majority of the music. What most average listeners likely call bass is way above 50Hz. All I can say is listen to an isolated 100 Hz subwoofer to get an idea of the tones that you think your going to miss. If you prefer that as a major element in your music then you need to consider it. Therefore don't worry about it unless you really love a lot of sound below 100Hz then you can always get a sub to augment that part of the "music".