Just speaking from experience here, and the pattern that Rockstar has of releasing GTA games, since GTA for DOS.
GTA is usually released in October. GTA 1 was October of 1997 if I remember right, London 1969 and London 1961 were October (I may be wrong and it was earlier '98 ) GTA2 was October, GTA3 - October, GTA:VC October.
See a pattern? These are all off the top of my head and I'm sure a little research might say differently. But most were released in October. 1 or 2 of them were bumped a few months back, but I think orginal release dates were in October. The plan at least was there the follow through was not.
As far as news on SA, really the only thing you can bank on is that when September hits you MAY see something about it somewhere. Rockstar is so secretive about what they are doing the US government should take be taking lessons from them.
No matter what anyone says, or what an article says, unless it has come directly from Rockstar, I wouldn't put my money on it that its completly true.
And even then, remember Rockstar has been known to release false information to throw people off, so really I guess the only to see what SA will be, is to wait till October and hope it dont get bumped.
Just my three and a half cents