Powell's stats for 1900 are mostly from Play-by-Email games, which definitely impacts the data. It's not as reflective of the web-style of Diplomacy play. PD's stats are more likely to resemble what you'd hypothetically see on sites like vDip.
PD maintains an archive of all of its finished games, and you can get the statistics if you have a web scraper and are handy with Excel.
The following are a quick summary of stats for samples from 1900 and Classic, only looking at full-press games run without extra variants. GPR is calculated on a 180-point basis (180 for solo, 90 for 2-way, 60 for 3-way, 45 for 4-way, 36 for 5-way, 30 for 6-way, 0 for 7-way or loss).
There were 232 completed games of 1900.
F: 17 solos, 170 losses, 24.69 avg GPR
R: 13 solos, 170 losses, 22.27 avg GPR
I: 20 solos, 163 losses, 28.19 avg GPR
G: 29 solos, 61 losses, 38.04 avg GPR
A: 15 solos, 169 losses, 23.72 avg GPR
T: 10 solos, 180 losses, 18.22 avg GPR
E: 16 solos, 171 losses, 24.10 avg GPR
For comparison, I took a sample of 178 recent classic games from PD before my scraper allowance ran out:
F: 18 solos, 121 losses, 32.19 avg GPR
R: 24 solos, 123 losses, 35.39 avg GPR
I: 5 solos, 146 losses, 14.66 avg GPR
G: 10 solos, 125 losses, 25.20 avg GPR
A: 8 solos, 141 losses, 17.70 avg GPR
T: 11 solos, 126 losses, 25.37 avg GPR
E: 14 solos, 125 losses, 28.48 avg GPR