I agree with you that the reasons for my 4:46 first marathon time were a lack of mileage (topped out at only 30 mpw), along with a severe case of cramps beginning at mile 17 (also probably due in part to inadequate training, as well as an unusually warm and humid March morning). The half time of 2:12 is where I finished the first 13.1 of that marathon (and the humidity was already taking its toll by then), so the last 13.1 took 2:34 worth of run-walking. That's 11:45 pace for the last half, including all the walking, after running the first half at 10:04 average.
Hence, my selection of a training plan that goes up to 55 mpw, nearly double what I did the first time. It would not surprise me if merely adding another 25 miles a week were enough to get me under four hours, and maybe even faster. But I don't object to Pete throwing in some tempo/VO2 work, if only to combat the boredom of doing the same thing over and over again, five to six days a week for six months. Besides, I like running fast
Hey, I'm still building my base; I know that. I may need to look at going beyond 55 mpw even during this training cycle. I started training on July 7, 2007, from zero, and finished a marathon exactly 34 weeks later. A lot of people would argue that I should have built the base for 12-18 months minimum before I even attempted a marathon, and there is validity to that argument. But I set myself a challenge last summer and succeeded in meeting that challenge in 34 weeks. Now I have another challenge out there -- sub-four -- and that's why I'm on this site, to get your input on how to get there. Then I set my sights on a starting line spot in Hopkinton. Then again, with more mileage AND speed, maybe Hopkinton is closer than I think.