What FPGA & memory chip/type should i use in order to save ADC data fast enough?

Hi, i am working on a DSO with the ADC (ADS4225) Dual channel 12bit @ 125MS/s each. I want to accomplish saving both those two 12bit channels with a FPGA into a memory chip. I have not devoted too much time on interfacing FPGAs with memory chips but i have been experimenting with a DE0-nano with a FPGA EP4CE22F17C6N on board and a SDRAM.

The ADC data (both channels) will be sent to the FPGA via 6-LVDS channels at 500MS/s when both channels are clocked at 125MHz.

Can this FPGA save the data i want as fast as it is required to a DDR or DDR2 (faster than SDRAM) so that both channels can be filled with data until the memory gets full?

Do i need to consider another FPGA?

Would you be kind to suggest a memory type or even a specific chip?

Are the ALTMEMPHY megafunction controllers suitable for what i need?

Regards

Manos Tsachalidis