I really think the answer to this will vary person-to-person because a lot of it will be how your body responds and recovers and it also will depend on how one defines "long run" but I tend to do better with more days off, too.
I chose to do a friday, saturday, sunday cluster because this most closely simulates race day fatigue. Plus, if I ever had a tune up race along the way, I could cut out the friday run and feel amazing on saturday.
I trained for a 100 by running 4 days per week but I was actually running twice on the weekdays.
Mon: OFF
Tue: 7 miles in the morning, 7 in the evening
Wed: OFF
Thur: OFF
Fri: 7 miles in the morning, 7 in the evening
Sat: Long run
Sun: 3/4th of Sat
Does this help? We can get into more specifics if you'd like, just ask.
~Toby