Whisky, thanks for the link to a very useful website! It's really good for comparing high-latitude vs low-latitude flights, and "low-30s" cruise altitude radiation vs "high-30s" radiation. Just to show some sample comparison data, here are some trips with a flight time duration of approx. 8 hours, using the month of January 2002, and using FL330 as a "lower altitude" sample, and FL370 as a "higher altitude" sample. Flight times are Takeoff to Landing, not gate-to-gate and reflect typical January cruise wind conditions :
Miami – Madrid (Flight time 7+55)
FL 330 entire cruise – 23.72
FL 330/FL 370 split – 27.48
FL 370 entire cruise – 31.53
London – Chicago (Flight time 8+10)
FL 330 entire cruise – 31.62
FL 330/FL 370 split – 37.23
FL 370 entire cruise – 42.71
Miami – Rio de Janeiro (Flight time 8+00)
FL 330 entire cruise – 16.53
FL 330/FL 370 split – 19.20
FL 370 entire cruise – 21.43
London – Barbados (Flight time 8+10)
FL 330 entire cruise – 22.10
FL 330/FL 370 split – 25.01
FL 370 entire cruise – 29.10
Interesting information !