New to middling - how big of an edge is needed

[Scruff]

I've read the FAQ and a few posts, and I want to try middling some games - so I'm wondering what is needed in terms of a spread.

For example, if one team is favored by -2.5 -110 on one site, and -3 -110 on another, you are basically getting 10:1 that the team wins by exactly 3. Is that enough of an edge? I'm assuming it isn't. But what is considered a minimal middle?

Thanks for any help. Bonus points if you can say minimal middle 5 times really fast . . .