If you do the same thing constantly, you'll start to plateau. Varying distances, speeds, rest periods etc will encourage your body to adapt to different outputs. One thing I will say though; be careful if you've not built up to that level of running. Lower limb injuries are the biggest factor for recruit injuries. Off the top of my head, I think it's responsible for almost half of all injuries sustained by nods.
@The guide will be able to confirm / correct on that.
Make sure that what ever program you choose to follow, you build in incremental improvements. So look at your program as a cycle, you've got Week A and Week B.
Cycle 1
Week A:
1x6 miler @ 10:00/mi
1x3 miler @ 8:00/mi
5x800m sprints @ 3:50/mi. 5 min rest.
10xhill sprints @ best effort. 3 min rest
Week B:
1x3 miler @ 8:00/mi
10x hill sprints @ best effort. 3 min rest.
5x800m sprints @ 3:50/mi. 5 min rest
1x BFT @ best effort.
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Cycle 2
Week A:
1x6 miler @ 9:45/mi
1x3 miler @ 7:45/mi
5x800m sprints @ 3:45/mi. 5 min rest.
10xhill sprints @ best effort. 2:45 min rest
Week B:
1x3 miler @ 7:45/mi
10x hill sprints @ best effort. 2:45 min rest.
5x800m sprints @ 3:45/mi. 5 min rest
1x BFT @ best effort.
--------------------------------------------
Cycle 3
Week A:
1x6 miler @ 9:30/mi
1x3 miler @ 7:30/mi
5x800m sprints @ 3:45/mi. 4:30 min rest.
15xhill sprints @ best effort. 3:00 min rest
Week B:
1x3 miler @ 7:30/mi
10x hill sprints @ best effort. 2:45 min rest.
6x800m sprints @ 3:45/mi. 5 min rest
1x BFT @ best effort.
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etc etc. That's a quick example of cycling / incremental improvements. Notice that not all the variables change though. Either decrease the rest time, or the speed, or the rep count. Never all three together, or you'll end up over doing it without realising.
The key with training and incremental progression is to leave your ego at the door. Just because a session doesn't feel like it's too difficult and you can push it harder, doesnt mean you should.
Anyway, I'm done rambling. Get running