I just did a sample calculation on matrix.itasoftware.com, making each leg of the flight on a Tuesday - purely arbitrary dates since Tuesday are usually cheaper.
Flying Delta through Japan (no Hawai'i stop) is fastest at about 16 hours total flight time each way.
Stopover in HNL on the way there: $1272, about 18 hours to BKK and about 16 on the way back total flight time.
Direct through Haneda: $1058, about 16 hours each way. It was $215 more to route through HNL on the way there.
Here's the sample itinerary through HNL, just to get you started.
Portland (PDX) to Honolulu (HNL) — Sun, Aug 9 Alaska Airlines 833
Dep: 7:05 am Arr: 9:55 am 5h 50m
Honolulu (HNL) to Tokyo (NRT) — Sun, Aug 9 Delta 579
Dep: 1:10 pm Arr: 4:00 pm 7h 50m
Layover in NRT Mon, Aug 10 1h 55m
Tokyo (NRT) to Bangkok (BKK) — Mon, Aug 10 Delta 584
Dep: 5:55 pm Arr: 10:45 pm 6h 50m
Bangkok (BKK) to Tokyo (HND) — Tue, Aug 18 Thai Airways 660
Dep: 1:00 pm Arr: 9:10 pm 6h 10m 2h 55m
Tokyo (HND) to Seattle (SEA) — Wed, Aug 19 Delta 580
Dep: 12:05 am Arr: 5:34 pm 9h 29m
Layover in SEA Tue, Aug 18 1h 26m
Seattle (SEA) to Portland (PDX) — Tue, Aug 18 Alaska Airlines 2047
Dep: 7:00 pm
Arr: 7:47 pm
0h 47m
Portland (PDX) to Honolulu (HNL) — Sun, Aug 9 Alaska Airlines 833
Dep: 7:05 am Arr: 9:55 am 5h 50m
Honolulu (HNL) to Tokyo (NRT) — Sun, Aug 9 Delta 579
Dep: 1:10 pm Arr: 4:00 pm 7h 50m
Layover in NRT Mon, Aug 10 1h 55m
Tokyo (NRT) to Bangkok (BKK) — Mon, Aug 10 Delta 584
Dep: 5:55 pm Arr: 10:45 pm 6h 50m
Bangkok (BKK) to Tokyo (HND) — Tue, Aug 18 Thai Airways 660
Dep: 1:00 pm Arr: 9:10 pm 6h 10m 2h 55m
Tokyo (HND) to Seattle (SEA) — Wed, Aug 19 Delta 580
Dep: 12:05 am Arr: 5:34 pm 9h 29m
Layover in SEA Tue, Aug 18 1h 26m
Seattle (SEA) to Portland (PDX) — Tue, Aug 18 Alaska Airlines 2047
Dep: 7:00 pm
Arr: 7:47 pm
0h 47m