Hard to say unequivocally old chap - when I upgrade a ROM I tend to go the whole hog and do the kernel and modem too. . . .so while the drain with JPY was probably higher for the reason mentioned above, I'd say the battery life is actually better now, so the loss has been offset by gains in the kernel and ROM itself. To be fair though, I always switch 3G off when I'm not using the phone, and wifi reconnects in about 2 seconds from lock.
Phone off charge yesterday morning, and it's currently showing 77% - not bad for 30-odd hours!!
Bloody amazing, I'd say. Wow!
Whatever combination you're curently using, it's legendary. Samsung should bottle it. :D
Mine's sitting at 75% after 13 hours which isn't too shabby considering 3G has been enabled for 100% of that time.