So here's the logic. I reckon that to run the marathon in under 3 hours I'm going to need to be 100% fit, and weigh no more than 150. I'm 5' 9" by the way - which might surprise the many friends that always thought I'm 6' 2" ;) Carrying any extra weight on race day is a major impediment to a fast time. A pound or two might not sound a lot, but you imagine running 26 miles with a bag of sugar in your hand. Or belly. Hence, my not so thorough analysis has concluded that for every additional 1lb in weight, I increase my marathon time by 5 extra minutes. Likewise, for every 10% below my target peak fitness level, I'll give up another 5 minutes huffing and puffing around San Jose.
Today - I'm weighing 157 and I felt something pop in my calf after a light 40 minute jog this morning. So comparing this with previous weight and fitness levels, I'm estimating that I'm at 35% of peak fitness, and 7lbs off my target weight. Add that up and I'd expect to run a 4:07 if the race was on tomorrow. Think I'll plot this graph every Thursday and see where it leads.