I have experience putting in 100 mile weeks in singles and putting in 130 miles a week with doubles and single mileage in the 90 range. Below is a snippet of some of my training earlier this year where I was running 100 in singles. I did not find it as effective as running double days. I began to feel stale and between runs was so long I felt like it took me longer to "warm up" at the start of each run. Thus, I don't feel I was getting as effective of workouts. I also was maintaining a higher weight during this time period, I think because I didn't get that boost to my metabolism each morning. If you have the time and can make it happen, doubles seem more beneficial to me. (The reason I didn't run doubles during this period was due to laziness before work.) The wheels fell off shortly after this snippet.
Hope this helps.
Day - type of run - mileage - time - notes
Monday Base 14 92 PM
Tuesday Base 16 108 PM 5.5 wu, 5.1 @6% Grade on TM 33:40, 5.5 cd
Wednesday Base 13 86 PM
Thursday Base 13 74 PM Last 6 in 30:30
Friday Base 13 86 PM
Saturday Base 12 86 PM
Sunday Base 21 132
Total Mileage 102 All Singles
Monday Base 12 81 PM
Tuesday Base 13 92 PM
Wednesday Med LSD 16 110 PM
Thursday Base 13 93 PM Golf Course, Ice Bath
Friday 5 Mile Tempo 18 127 AM 3wu,5mi temp 26:20, 3 cd PM 60 min
Saturday Base 12 79 AM
Sunday Long LSD 22 151 NOON GMNP 90 dirt, 40 asphalt, 20 concrete
Total Mileage 106 Singles=99
Monday Base 12 85 PM Half at GMNP Half
Tuesday 8x1m (4m off) Fartlek 13 85 PM
Wednesday Med "Sunday" Run 16 104 PM
Thursday Base 12 89 PM to GMNP
Friday Base 11 75 PM
Saturday 1 mile race 16 110 AM 2mi so, 30 min wu, 1mi race 4:11 last 800 in 1:58, 60m cd
Sunday Long "Sunday" Run 22 130 43 AM last 3 in 15:20
Total Mileage 102 Singles=100
Monday Base 13 97 45 PM All Dirt GMNP w/ headlamp
Tuesday Base 14 92 40 PM
Wednesday Med LSD 16 114 42 PM
Thursday Base 12 80 42 PM
Friday 5 Mile Tempo 17 111 39 AM 3mi PM 5wu, 5 tempo 26:12,4 cd
Saturday Base 14 134 42 2 Wu 6@6% TM 2 cd,2 faster, 2 cd
Sunday Long LSD 22 152 43 AM
Total Mileage 108 Singles=102
Monday Base 12 81 43 PM
Tuesday Med "Sunday" Run 16 100 39 PM 16.51
Wednesday Base 16 109 44 AM 74 min 11mi PM 35min YMCA
Thursday Base 14 87 42 PM
Friday 8x90on 210off Fartlek 13 86 41 PM Forest Park
Saturday Base 13 86 38 AM
Sunday Long "Sunday" Run 22 140 39 AM Hill Road 14mi dirt
Total Mileage 106 Singles=101
Monday Base 15 101 44 AM 35 min OR PM Late
Tuesday Base 13 93 44 PM
Wednesday Med LSD 16 115 41 PM 16.51
Thursday Base 10 86 44 PM
Friday Base 11 79 43 PM
Saturday 5 mile tempo 15 95 40 AM 5wu 5 tempo 24:36, 5cd
Sunday Long LSD 21 150 43 AM
Total Mileage 101 Singles=96
Monday Base 13 91 43 PM
Tuesday 8x2min 3rest Fartlek 13 86 41 PM
Wednesday Med "Sunday" Run 16 105 43 PM 16.51
Thursday Base 12 90 43 PM
Friday Base 11 75 41 PM Dirt behind house
Saturday 10k Race 15 96 41 AM 2 mi so, 4 mi wu, 10k 30:56, 3 mi cd
Sunday Long "Sunday" Run 21 141 43 Noon
Total Mileage 101 Singles = 99
Monday Base 13 86 44 Aqua-4 loop
Tuesday Base 13 86 42
Wednesday 5x1600@4:45,3min r 13 80 40
Thursday Base 13 85 42
Friday Base 12 82 42 Aqua-4 loop, HOT
Saturday 7 Mile Tempo 15 95 41 4 x 1.75 loop 7 Mile Tempo 35:37
Sunday Long LSD Run 22 147 44
Total Mileage 101 Singles=101
Monday Base 13 83 42
Tuesday Base 13 85 40
Wednesday 8-12x800@2:18 90s r 16 100 40 AM 4 mi PM 9 x 800 2:20,17,18,18,20,20,18,17,17
Thursday Base 13 82 43 loop plus addon
Friday Base 11 74 41 recovery 6 good strides
Saturday Base 15 97 41 10k 31:01 300 for win 4 wu w/ 2 6 min miles
Sunday Long "Sunday" Run 20 126 43
Total Mileage 101 Singles=95