As you're building volume, don't worry about pace at all. Worry about time on your feet. Once your long run is up to 2 hours or so, then you can see what pace you're going and gradually bring that pace up through improved fitness.
Your body has a much harder time coping with the amount of time spent running during a marathon than it does with the physical exhertion of the race itself.
I would agree that time spent running will do more than pace/