Jason, your threads are really catching my attention. I think if you want to run 4:30 - 5:00 per km for your long run, go ahead. The trick is it won't directly help you to run your marathon race pace. However, it will give you a stronger base which will help you to run better in the long run.
There are some things you should know about Japanese training. First, the Japanese start training hard, harder than 99% of U.S. elites, in high school. They run high mileage, over 200 KM per week, all the time. They often do 4 hard workouts a week. Because of this training, they are always very aerobically fit. But they are also very tired, and often sick or injured. Usually when they run well they are coming off of an injury or illness, or a serious race taper. The ton of miles you do with Japanese training will help in the long run, but it will probably make you tired in the short term. When I ran in Japan, I usually ran 120 miles a week, 150 at training camps, and my teammates were almost always higher. Some of them NEVER took a day off. The training is also very progressive, starting with longer and slower (say 40KM at 3:30/KM) to faster and shorter. Before the New Year Ekiden which is their most important race, our team did 8K @ 3:00/K, then 5 min recovery and a 3K time trial, which was run in about 8:20.
To summarize, just about any training will be good for you in the long term, but it may take some periodization to run your best off it. This is where the Japanese have an edge on us. The coaches will have a grand plan of mega mileage with a couple of key season and races a year instead of seeing $$ on the race schedule every weekend. Train hard, high mileage, where you are so tired you can hardly run. Do this for months, even years, then start race specific training with more rest. This, I believe, will you give your best performance for races over 10 miles.
David