score:6
I found it!
When Michelangelo was wending his way from Florence to Rome, to assume the charge of finishing St Peter s church, his servant related that on reaching the summit of the Apennines near Poggibonsi he turned his horse and sat gazing long and intently upon the dome of Brunelleschi, the giant cupola of the Florentine cathedral. After some time he was heard to growl, "Better than thee, I cannot; like thee, I will not!" The result was the dome of St. Peter's.
The source was Form and function: remarks on art, design, and architecture Greenough, Horatio.
Whether Michelangelo actually said this is another matter...
(Come to think of it, misremembering a quotations from some obscure source like I did and then passing it on as authentic is probably how these bogus attributions come about in the first place!)