40" is going to be cutting it close. Irwin seating lists a minimum front to back spacing of 36" for their Springfield line. That will probably be a bit tight. I have the high back rocker version of the Springfield (which needs more space to begin with) and my back row is 52". This is tighter than I wanted, but not bad. I would have liked to get them off the back wall more and had a few more inches of leg room.
That said, I can't recommend the Home Theater version of the Springfield enough. People are always telling me that they are surprised how comfortable my chairs are. You can see pictures in my build thread linked from my sig.
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