From personal experience and the experiences of several of my friends, SA Home Loans tends to be much more flexible and willing to negotiate interest rates than the banks.
Recently, a friend of mine called them and offered to move her Nedbank home loan to them if they offered a better interest rate. She was paying 12% at Nedbank and they dropped her interest rate to 10.2% and covered the bond costs.
And when I was buying, SA Home loans made me an offer of prime rate. I asked them if they would drop the lending rate by 0.25% and they said they would do so if I increased my deposit by a certain amount, which I did. So, after approval in principle, they certainly are willing to negotiate interest rates depending of your, and the property's, risk profile, as well as the deposit you're prepared to put down.
Also, I've had my bond with them for almost seven years and I'm very happy with their service. You really should give them a call...