As you noted, the generally-cited Ashkenazic haftarah for Parshat Pekudei is from Melachim I 7:51-8:21. However, there are two additional customs to be aware of, which may go some way to answering your question.
There exists an Ashkenazic custom in the Diaspora to read Melachim I 7:40-8:1 as the haftarah for Pekudei. This is brought down by Maharil (Customs of the Four Parshiyot) in the name of Maharash, and is subsequently quoted by Elya Rabbah (685:23). (In contrast, this custom is not mentioned by Levush (685:6).)
Maharil explains the rationale for this custom, is that in any event Melachim I 8:2-21 was read as the haftarah for the second day of Sukkot, as opposed to Melachim I 7:40-8:1 which would not otherwise be read at all.
The Sephardic haftarah for Parshat Pekudei is generally assumed to be from Melachim I 7:40-50 (see e.g. the Wikipedia list you quoted in your question) i.e. the selection normally listed as the Ashkenazic haftarah for Parshat Vayakhel.
R. Y M Tucazinsky writes in Sefer Eretz Yisrael (16) that the custom among the geonei yerushalayim is to read Melachim I 7:40-8:21. He explains this as an application of Maharil's ruling (to read Melachim I 7:40-8:1) to the situation in Israel, where there is no second day of Sukkot, and thus neither Melachim I 7:40-8:1 nor Melachim I 8:2-21 are read at other times during the year. Thus, on Parshat Pekudei the custom is to read both.
In contrast, Aderet in a letter quoted in Yerushatenu vol. II p. 184 writes that he was the one to introduce this practice. He writes that he found the Ashkenazic custom in Jerusalem was to read Melachim I 7:40-50, like the Sephardic custom. Aderet believed that the more correct practice was to follow the widespread Ashkenazic custom of Melachim I 7:51-8:21. However, so as not to (totally) depart from the original custom in Jerusalem, he instructed that both haftarot be read (i.e. Melachim I 7:40-8:21).
As an addendum, we can address a leap year which contains two shabbatot chanukah (year type זשה), in which case Melachim I 7:40-50 is read as haftarah on the second shabbat chanukah.
In such a year, Birur Halachah vol. 6 (Orach Chayyim 428) quotes R. S Z Auerbach and R. S Deblitsky as ruling that the haftarah for Parshat Pekudei comprises only Melachim I 7:51-8:21. This seems to follow R. Tucazinsky's approach: since Melachim I 7:40-50 has already been read earlier in the year, there is no need to read it again.
However, somewhat paradoxically, R. Tucazinsky himself had written in Sefer Eretz Yisrael (ibid.) that both haftarot (i.e. Melachim I 7:40-8:21) are read, even in a year of type זשה.
This position (to my mind) actually accords better with that of Aderet. The Sephardic haftarah for Parshat Pekudei is always Melachim I 7:40-50 (even in a year where that was read on the second shabbat chanukah). If the Ashkenazic custom in Jerusalem was in line with this, then Aderet's ruling to add Melachim I 7:51-8:21 on top of the pre-existing reading would apply in every year-type, even in a year of type זשה with two shabbatot chanukah.
As a second addendum, we can address a leap year in which Parshat Shekalim is read on Pekudei (year types החא and השג), in which case Vayakhel is free to receive its own haftarah.
In such a year, almost lists of haftarot that I can see (e.g. on Wikipedia) list only Melachim I 7:40-50 as the haftarah for Vayakhel. However, it does seem that even for Vayakhel, there are those in Israel who would read the full "double" haftarah of Melachim I 7:40-8:21. (See for example the claim here that R. Tucazinsky in his calendars for leap years always listed Melachim I 7:40-8:21 as the haftarah for either Vayakhel or Pekudei, whichever was available. If anyone has access to an old luach le-eretz yisrael for a year of type החא or השג (the most recent occurrence was 5774) I would love to see it.)
Again, we can line these two positions up with the two reasons we have given for the custom to read the "double" haftarah for Pekudei.
If the reason is to make sure we don't miss either of the two readings in a given year (R. Tucazinsky), then in Israel we would also read them both for Parshat Vayakhel. (In this respect, R. Tucazinsky is consistent - in any leap year, in Israel he tells us that we always read Melachim I 7:40-8:21 on whichever shabbat it is possible to do so, thereby ensuring we miss neither reading.)
This is also consistent with the diasporic practice which seems to have developed in Frankfurt to read as the haftarah for Parshat Vayakhel Melachim I 7:40-8:1 (i.e. the 'classic' haftarah for Vayakhel with two additional verses; note that this custom was never mentioned by Maharil). Presumably, this was done in order that all of the verses would be read during the year, relying on the second day of Sukkot to read Melachim I 8:2-21. (See, for example, Zichron Chanoch p10.)
However, following the approach of Aderet, we can understand why the "double" haftarah custom only applies to Parshat Pekudei, and not to Parshat Vayakhel. For Pekudei, where the Sephardic custom is to read Melachim I 7:40-50, the Ashkenazim then extended the reading by adding 7:51-8:21. But for Vayakhel, the Sephardim have a different reading (Melachim I 7:13-26). This reading seems never to have been adopted by the Ashkenazim, in which case they would simply read the longstanding, traditional Ashkenazic haftarah for Parshat Vayakhel, i.e. Melachim I 7:40-50.
