I would say that if, and this is where you have to make the decision, you are able to run 2 hours every week and not feel drained, then do the 2 hours. The return from the extra time makes it worth the extra time. I work with a number of HS runners who find 2 hours weekly year round, a challenge. I also work with lots of runners who try to fit in running around an active life, for them the 2 hours every 3rd week allows for more recovery and scheduling. If you can do the weekly 2 hours and go on about your life without needing a nap after the run, then keep it up. When Dr Snell was at the Lydiard Foundation kick-off, he made a strong argument for the benefit of doing as many 2 hour runs as you can handle. He stated, that even for him as an 800-miler, the two hour runs were THE most important training runs he did.