Kelly told reporters: "When you go through it and you're going as many times and as many evaluations, there is an up day and a down day, and up day and a down day.
"So who consistently over the time has played at the highest level? But to say one day this guy was above and then it drops
"I thought all three of those guys today (Vick, Foles and Barkley), and then the little snaps that Dennis [Dixon] got, they played pretty well today."
The Eagles begin their pre-season campaign against the New England Patriots next week.