Hi All,
I would vote in the Colluricincla megarhyncha camp myself based on the following features:
To start with, there are relatively few choices based on location. They've all been mentioned. White-breasted Whistler, Grey Whistler, Mangrove Golden Whistler, and Little (Rufous) Shrike-thrush.
My impression of Grey Whistler is that it is a slimmer, smaller-billed bird than the mystery subject, and lacks ochraceous color to underparts. The few images of White-breasted Whistler (alas, a bird I've yet to see in life) show a bird with a thicker bill than the subject bird, and again with paler ground color to underparts, and thinner, more sharply defined streaking to underparts. They also don't seem to show particularly paler, contrasty lores. Mangrove Golden Whistler is more yellowish below, and without the paler lores, and lacks the delicate breast streaking visible on the mystery bird. I think it is also shorter billed than the subject bird. On the other hand, Little Shrike-thrush fits pretty well, so long as one considers the subspecies involved. Birds from the Top End parvula differ from those Tom would see in s.e. Queensland, in having a dark bill. The bill shape matches well with photos and illustrations of parvula, and the ochraceous tones to underparts, breast streaking, and paler lores also seem to fit as well.
Chris