mrburnette:
You may also consider moving the data to a 2nd atmega which is managing the SD card.
Pardon me but I could not get one basic idea behind this. If writing latency to the SD card is the problem, then how can moving the data to second atmega solve the problem, because the data will be read at a higher speed but will be stored at a slower rate. I feel for real time data acquisition incoming and outgoing data should be same.
I am very new to arduino and all this stuff so I could not get what you meant by not needing to allocate 512 Bytes to the sector buffer is a big advantage. So maybe could you please elaborate it a bit?.