grammatical number - Plural or singular when stating that an amount is enough

A colleague of mine corrected the following sentence in a text I had written:

A handful of iterations was generally enough for convergence.

According to her it should be:

A handful of iterations were generally enough for convergence.

I am, however, confident that my original usage was correct, but I am unsure how I should motivate this.

EDIT: What made me think it was singular was not "a handful of". I thought it would be correct to say Five iterations is enough. because it is a statement about the number of iterations rather than the iterations themselves. When googling to find an answer I found a television series called Eight Is Enough. Is that correct because the noun is left out? Compare the sentences: Three friends are ideal. and Three friends is ideal. I would have thought that the first sentence means that there are three persons who are ideal friends, while the second sentence means that three is the ideal number of friends to have. But maybe my intuition is really off here.

EDIT2: Here it is stated that:

*Subjects expressing periods of time, amounts of money, or quantities may take either singular or plural verbs depending on whether represent a total amount or a number of individual units. For example, "Four weeks is not enough vacation time" and "Two days have passed since I asked for your response."

Isn't the first example here quite similar to mine?