If you want to hop on the 4L Chinese domain craze here is how it works:
Typically the Chinese domain buyers like balance.
With 4L's the LLLL is divided in half like LL | LL.
So the reason why BJXT sold for $5k was that BJ | XT could stand for any business in Beijing (BJ) using the letters XT. SInce X is a very premium letter, and highly used in PinYin it's not a stretch to assume that a business uses the abbreviation XT based in Beijing.
So was it worth $5k, yes... will they sell it for a profit... yes. I've dipped into $5k LLLL's before, not a fan of the profit margins but who know how much anyone will pay at any given time.
Letters not to buy A,E,I,O,U,V... but why?
These letters/sounds typically don't appear in Chinese PinYin; they don't make any words for them. So BVXT no longer makes any sense for a Chinese buyer.
Of course this is NOT the standard for English speaking 4L buying. Typiclaly English speakers love pronounceable or exact match 4L's - like WERK that sounds like WORK which sold for $200k+.
Let's be real with ourselves when we are saying things are 'premium' and 'pronounceable'. Thats why people use CVCV as a purchasing guide, because typically 4L's that are CVCV can be pronounceable within our language.
Now LICQ sounds like Lick, thats a pronounceable brandable domain.
You should also use the mentality that the Chinese buyers use when buying 4L's... what could my 4L say, or be an acronym for?
'Z' and 'X' 4L's could be picked up for cheap a few years ago because in the English language, those letters don't make many good words.
The A,E,I,O,U,V does not apply for English buyers. Which is good because you can pickup 4L.com A,E,I,O,U,V domains on the cheap because people are being told that they are 'bad' - they aren't.
As with all domains, justify your buys with logic. I hope this helps.