I'm going to hope that hito will chime in if I get any of this wrong.
If it were written as 五聖強の塔 instead, it
could be "Five Sacred Powers," but that's with 聖 being used as a prefix. As actually written, 聖 follows 強, so 強 is modifying 聖 rather than the other way around.
I still think 五強の塔 would be best written in English as "Pagoda of the Five Powers," but 五強聖の塔 is almost certainly "Pagoda of the Five Mighty Sages" -- though I don't think anyone would hold it against you if you used "Priests" instead of "Sages" if you feel that would fit better.
Personally, I'd go with "Sages." 老師 -- one of three ways of saying "priest" in Japanese that is coming to mind for me at the moment -- also carries the "sage" meaning (this was the word that became "maester" in the English translation of FFX, by the way), while 司祭 refers to Christian priests and 神主 refers to Shinto priests.
Obviously none of those are terribly similar to 聖, while 聖人 is (meaning "saint," "sage" or "holy man"). For the sake of mentioning, the latter is also apparently synonymous with 賢者.
Given that you fight Godo and the rest on the grounds of Wutai's primary shrine (that's what the building next to the pagoda is identified as in the Ultimania Omega; pp. 285-286), and given that they're apparently in charge of maintaining and protecting the premises as well as the sacred materia of the Wutai deity, I definitely think that something along the lines of "sage" or "priest" is called for.
As for the accuracy and applicability of "sage," keep in mind that this is Final Fantasy.
Just look at the Sage job class:
http://finalfantasy.wikia.com/wiki/Sage
Guys like Tellah belong to that group, as do, arguably, the maesters of Yevon. Those guys -- especially Seymour and Kinoc -- are anything but pacificists, and at least two of them are magic users and summoners.
Your call, of course, but that's my assessment.