I think you are on the right track...if this is the first time you've ran this kind of mileage - understandable that you feel a little sluggish (slower). I am finding more and more that when my mileage goes up to keep doing some quality (like your tempo day). I would even go further with that and say don't be afraid to do 2 to even 3 of those a week (don't think of them as hard workouts, but as efficiency runs). Or do 2 tempos with one track workout (nothing searingly fast - just a day of some controlled 200's will do - just to keep the legs quick). As you do these workouts, I think your alternate slow days can actually be slower...7:00 pace should and probably is very easy for you, but as you start doing more tempos, if tired on the easy days = kept them easy. For example, I might run my tempos 5:50-6:05 pace but I will go even longer at this pace. But then on my recovery days, I may only run 7:30 pace sometimes slower based on how I feel. So I might suggest pushing the tempo pace more or going longer (so you will be more tired) and slowing the easy day pace some (7:30-8:00) there is value in the slower fat burning paces - especially for the marathon.
the improvement you are looking for will show up in the tempos:
the tempos are where it is at - this is where the improvement will start to show up. Marathon pace is a good guide, but don't be a slave to any set pace on your tempos...just let them happen...you may be slower at times, but you may also start to get faster at times (especially toward the end). don't be afraid to open up the last couple of miles and start hitting 5:30 or so. the more miles you do at these faster but still comfortable paces - the more efficient you will become.