Never tried the J5, so I can't comment on its AF - but my issue with the V3's AF is not how fast it is (continuous AF at 20fps is more than fast enough). So with regards to NR's rumored V4 spec of "faster AF" - I would hope that it's NOT "faster", but rather that it's "more accurate". I've felt for over a year, now, that the central AF area on the V3 is too large, making it difficult to accurately focus on smaller subjects. Because the V3's AF point is (relatively) large - it tends to overlap smaller targets, thereby causing it to misfocus when backgrounds are bright, contrasty, or very budy. I would hazard a guess that any AF issues with the J5 is related. If Nikon can make the AF point(s) smaller on the V4 without sacrificing AF sensitivity in low light - that would make me a happy camper!