The SLT design drops about 0.5 EV in high ISO capability because some of the light is linked off for focusing.
I essentially see very little difference in image quality between my Alpha 900 and my Alpha 99SLT at low ISO. The Alpha 99 is much better at high ISO.
The Alpha 99 probably has an advantage in low ISO DR, but I have not been able to confirm it in any of my pictures, yet.
What that actually means is that the a99 is the fifth best overall camera ever tested by DXO. Most of the "points counted off" were for the "sports" calculation which measure high ISO capability. It still handily beats anything from Canon and has one of the three highest dynamic ranges of any camera at the business end of the ISO scale. More to a camera than its DXO sensor score but nice to know that Sony did very well. I already knew the camera was good, I shot with it all last week...