Assuming you cannot run fast, long, and high mileage during the same training cycle, which should be emphasized?

It's an individual issue, but having done all three, I'm pretty sure the answer for me is to run high volume. If I run over 55 miles per week, I see improvement in the longer races. If I add 1 tempo or VO2 workout to the mix, the speed is covered.

In the past, I've done a long run every weekend and around 50 mpw. It will get me into good shape, but not nearly my best for marathons. My last marathon(11-06), I was in Korea and couldn't run too far on weekdays(5 miles/day). So I'd do a 20-miler every weekend. It didn't really work too well. My marathon was 3:28. Granted, it was muggy and I am much slower in such weather, but had my conditioning been better, I would probably have run much faster despite less than perfect conditions. I must have run ten 18-22 mile runs preparing for that race-- all alone--and got to a point of hating the long runs.

On the other hand, my two best marathons were built on only 4-5 runs of 18-plus miles with a higher weekly output of around 55mpw. Seeing that I'm at 52 mpw base currently, I should be able to jump that to 65-70 once the snow clears. But I'll only do long runs every two weeks.

I'm planning on the Niagra Marathon in the Fall, so we'll see.