I would for sure look into it, it sounds easier to go from home in Japan → PSA Japan → home in Japan, than to go home in Japan → middlemen in USA → PSA USA → middlemen → home in Japan. It will involve less risk in shipping, might or might not have quicker turnarounds (absolutely no idea) and I now remember that I have read something about PSA Japan in the giant grading thread which is this:
www.elitefourum.com/t/the-giant-professional-grading-thread/30930/823
The prices seem to be different, I dont know if it is that significant with the value of the cards you are submitting. But I would definitely look into it, for now or for future submission if you have got more time on your hands.