@andywood, David has posted some reports about his SR600 rides, including SR600 Fuji (completed) and SR600 Nihon Alps (abandoned due to weather-related road closures):
Jan Heine wrote about his Nihon Alps attempt in the spring issue of Bicycle Quarterly (BQ#51). He had to abandon, but says he'll be back for another attempt.
As for my own schedule, I'll sign up for all the AJ NishiTokyo rides that don't conflict with my travel schedule, taking another stab at achieving Super Randonneur status (200-300-400-600 km in one season) in 2016.
I may have to sign up for additional 400 and 600 km events for backup, since I have only ever completed a 400 once (last year) and have DNF'ed on all three 600 events I participated in. Some other clubs' courses have less climbing but AJ NishiTokyo are like friends to me and most of their rides start and finish just 28 km from here.
Hopefully the new bike will help next year, but I'll have to see how much of a difference it will actually make.