Choosing a FPGA

Hi,

I am using a FPGA with a DDS board (AD9910). The DDS board has a parallel port where I can send a 16bit word every clock pulse. The DDS parallel port can latch onto data every 4ns. So far I have been using the deo-Nano board to send data every 20ns but now I want to maximize on the speed of data transfer. I would also like to store a list of 16bit words to the SDRAM on the board and then read it out every 4ns from the SDRAM to the GPIO headers. From what I have read on the deo nano so far, it seems that reading data every 4ns from the SDRAM on the deo nano board is not possible. I would be very grateful if someone could direct me towards a board where such speeds are attainable or tell me if it's possible on the deo nano and what all timing considerations I should take into account.Also, I need a Thanks!