This refers to Aquinas, Summa contra gentiles, 4.1, prooemium, where the phrase occurs twice.

The standard English translation of Book IV is by Charles J. O'Neil (New York, Hanover House, 1955-57). He renders this as "highest summit both times:

"quia omnes rerum perfectiones quodam ordine a summo rerum vertice Deo descendunt"
"since the perfections of things descend in a certain order from the highest summit of things—God"

"Et quia in summo rerum vertice Deo perfectissima unitas invenitur"
"And because in the highest summit of things, God, one finds the most perfect unity"
http://dhspriory.org/thomas/ContraGentiles4.htm#1

It's an accurate translation of "vertex", which means:
"I. whirl, eddy, whirlpool, vortex
II. eddy of wind of flame
III. top or crown of the head, and by transference:
B. 1. The head
2. The pole of the heavens
3. The highest point, top, peak, summit of a mountain, house, tree, etc."
Lewis & Short
http://www.perseus.tufts.edu/hopper/text?doc=Perseus:text:19...

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Note added at 48 mins (2015-02-22 18:27:37 GMT)
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And summus/-a/-um does of course mean "highest".

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Note added at 1 hr (2015-02-22 18:42:45 GMT)
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John I. Jenkins, who uses "supreme vertex" for this, is President of the University of Notre Dame and a very fine scholar. But I don't think the cognate, "vertex", is a good idea, since it is very rarely used in English in any context other than geometry, and the Latin vertex simply means highest point or summit. "Highest summit", following O'Neil's translation, is widely used by Aquinas scholars, as for example in the Oxford Handbooks of Aquinas:
https://books.google.es/books?id=PYXidm1an8IC&pg=PA60&lpg=PA...

And in many other places:
https://www.google.es/search?num=100&q="aquinas" "highest su...

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Note added at 3 hrs (2015-02-22 21:01:26 GMT)
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By the way, although it's not in the question, "hacedor de todas las cosas" corresponds to Aquinas's expression "creator omnium", and the epithet "Hacedor", applied to God, means Maker or Creator, but not Doer, or at least not in this case.

"Dicit enim Eccli. 24-12: dixit mihi creator omnium, et qui creavit me, requievit in tabernaculo meo."
"Et videtur a Platonicorum dictis exorta, qui ponebant summum Deum, patrem et creatorem omnium rerum"

These are from the same part of Summum contra gentiles, 4.1.