I have never flown Delta, but we flew Northwest a couple months ago. The "economy class" had the least legroom of any airline I have ever been on. The plane was old. It was just yucky in my opinion.
I think most planes seats that are similar width-wise, but I honestly think there wouldn't have been much room to install a seat RFing. DD didn't have a lot of room when her MA was installed FFing. In other words, she could very easily kick the seat in front of her. That was my experience with Northwest. The people were helpful, and there really wasn't any hassle in respect to flying with a Canadian seat on an American carrier. No one even asked to see the sticker. The reps at the gate made sure that we could pre-board, and even checked our gate passes before the plane arrived at the terminal to de-plane. Friendly - yes. Comfy-not all all.