I'm currently trying to get my miles consistantly over 100 mpw. 42 yr old male, married, kids, job, etc etc. It's not coming easily. Last winter I managed 10 weeks at 80 mpw and ran FIVE PR's in one race, a 1/2 marathon in March (5M,10K,15K,10M,13.1M). It was my 1st "real" race of the year. I've had a great year of running with PR's on everything I've touched and even managed a few wins. I hope to continue the trend. I'm back at it for 30 months after 22+ years off. (Gravity kicks in at 40) Anyway, if I do doubles, I can clearly manage more miles than if I run singles. I'm doing both weekly but feel that single longer runs help more. While I've been at this latest higher mileage phase only 5 weeks now, my longer runs are at 15-17 miles on Sunday. I try for 2 midweek runs of ~13 with the rest in doubles of 7M in the a.m. & 8M in the p.m. I plan to raise the weekend long run to 20-24 as I adapt.
I think the single runs of 13 feel like they're doing more than 2 runs of 15. My current marathon PR is a 3:03 w/o specific marathon training. With proper training, I'm hoping for sub 2:50 at Boston.
I see many of you guys who are in the 140 mpw range and am in awe. Any advice welcomed and appreciated.