Graham
here is JoeB's analysis on Nikolai Sutyagin's claims during Korean War:
http://www.acepilots.com/smf/index.php?topic=79
Joe visits also here and on WarBirds forum and have wrote more on Soviets' claims in Korea on these forums, by searching his messages from these boards You'll find more on Joe's research on Soviets claim accuracy.
Cheers
Juha