I would go with the morning arrival in BKK too - it will give you more day-time at destination and make adapting to the time difference easier. On the evening arrival you arrive late and straight to bed - which may not be easy if you slept onboard as well (after that journey it will likely be challenging to stack awake).
I’m (sadly) doing ORD-NRT-BKK and on the 11:45pm arrival in a month’s time, and not looking forward to it for those reasons.