My first two books came in at 206 and 495, next two (out this year and next) sold at 577 and 647 (we've done edits, but I don't know final wc- must look into that!). The two I sold last year were at 257 and 530 when they sold, but have yet to go through edits.
Interestingly, one of my newer PBs came in on the longer side, 850ish, with a slightly older protag (7-year-old), and two editors said it was more "beginning of a chapter book" than a PB. I'm going to be turning it into an early chapter book for one of them, but I couldn't help wondering if current trends (think: that NYT article!) affected their consideration.