What's some recent race results that you would believe are indicative of your current fitness level? With that I could make a suggestion on long run pace.
In the end though, finishing a run strong and faster than the beginning is a good thing and should happen on nearly every training run. It's a sign you're doing the training duration and pace your body can handle. The only caveat is to look at this over the long term as well as the short term. Because we don't want to "waste" our race effort on a training run. So let's say you do three 20 mile runs, all with the same intended pace. The 1st is a 9:00, the 2nd a 9:10, the third is a 9:20. This is also a sign of fading even if the run itself wasn't a fade within the run. It's a sign that you aren't fully recovering from week to week, and that come race day you might enter with too much fatigue for optimal performance.
In fact, I intentionally try to run progressive runs on nearly every training run. I want to train my body to accept going slow in the beginning and then progressively get faster. Train the way you want to race. Ideally the best strategy is an even split from beginning to the end. But it's soooo tough to know the correct pace at the beginning of the race, thus I advocate for the negative split because it ensures that you can't start too fast and surpass the Lactate Threshold too soon.