Qualcomm doesn't have a quad-core chipset available yet.
Unless this runs on their 8960 chipset [that has an integrated LTE chipset] the performance of any S3 released before Q4 2012 would probably be very similar to the Note.
The leaked pictures are just mockups, and it's a good thing too. They wouldn't sell many with a phone that looked like that.
I, for one, won't be changing - I've been through three Android phones in the last year and finally found one that I love enough to keep for some time.
My wife, however, will be able to upgrade in August, and at that time I'm guess it will be curtains for the iPhone 4; I think she'd like the HTC One X but no one touches Samsung's screens right now, so it might be this one, if it's out by then.