No way final release will be august as that's not the Fall, fall is from the september equinox, which is around the last week of september, like this year will be 23rd Sept. Apple said 4.1 would come out in fall last year, which they released in November.
beta 4 is very close to a GM, but still has some bugs, beta 4 saw windows getting wifi syncing, so i expect beta 5 as a minimum to counter for problems from that and from OTA syncing which was only tested for the first time with beta 4. I'm going with beta 6 in mid august, then GM beginning of september, at the earliest for around 3 weeks or so. they know exactly when they're releasing it, they said the Fall, so we have a rough idea, they won't release it any earlier even if the GM has been read for ages.