Predict my marathon time (Page 2)

Not to be a downer, but if your mileage was double what you're currently running per week (70 vs 35), I'd say 3:10 would be a stretch based on your race times. With low mileage it's not even feasible. A general rule is to double your HM time and add ten minutes for a marathon (that would currently be 3:22ish), but that is if you have done a solid marathon build. I consider a minimum of 50 mpw decent mileage for using the online race calculators, with 60-70 being ideal for most runners. 

To give you an idea, I ran a 3:09 in my first marathon 13 months ago, averaging 55 mpw over 18 weeks, and my 5k PR was around 18:15 at the time. I've since dropped my 5k time a bit more and am looking to crack 3:00 in NYC in two weeks.

You could try to go out around 7:15 pace, which is what a 7:10 equates to, but I don't think you'd be able to hang on. With 35 mpw, that infamous 'wall' will materialize around the 18-20 mile mark.

I'll go with 3:27:47 for your time.

I see. My question is this. For my first marathon in June, I really did 4 weeks of solid 40-45 mpw running. Before that I trained for the Mulholland Challenge (all cycling/climbing, 50-60 miles a pop) and the Wildflower (mostly hill repeats and more cycling), and I don't think I ever ran more than 12 miles. Wildflower was on 05/05, and I ran the marathon on 06/03. I did not train for 3 days after Wildflower, and I tapered the week before the marathon. I can share my Strava page, etc if wanted.

I did do a lot of cycling and a fair amount of swimming though prior to the Marathon (SD Rock'n'roll btw). This said, a 3:42 felt like a jog. Why would a 3:25 feel that much different after 4 months of hard (but mostly tri oriented) training? 

In any case, I will go out and do my best!

We've had lots of spirited debates here over the cross-over benefits of swim/bike training for running. But I don't think that anybody thinks that these non-impact sports prepare the body for the sustained impact of a marathon. That's what the mileage prepares your body for, and that's why folks aren't assuming that your tri training will have much impact on your marathon time, unfortunately.

17 minutes might not sound like a whole lot of time, but it is. 40 seconds per mile is a big difference.

Santa Clarita is a pretty flat course, so it's on the faster side, but not downhill enough.

I like 3:25 as well. Sounds like a very realistic time.

3:20 would be pushing it, and sorry, 3:10 will be impossible for you, even on a downhill course like Cal International with ideal conditions.

If this is your first marathon, 3:30 is a very realistic time.

I would aim to pace out at 3:25-3:30 and see how you feel at the 13 mile mark. Save the BQ sub 3:10 for the next training cycle - if you go for the gold right now, you'll definitely fall short and end up deathmarching the final 6 miles to a much slower time.  

While sneaking out around mile 10 and hitching a ride to mile 23.

I gotta say that most people predicted spot on. I ended up coming in at exactly 3:25. Here's the strava page for those interested - http://app.strava.com/activities/26939116

The temps ended up in the 80s around mile 21. I also somehow got stomach cramps after mile 16... that stinger waffle did not go down well this time, go figure. 

The new course ended up being not so flat. It also has about 20 or so of ended underpasses or short paseo bridges which ended up really grinding your quads over the long time. The last 3 miles were a sufferfest with the heat and all. 

In any case - thanks for your predictions. They helped me set the pace and the expectations.