C2050s are double width cards. There is only room for three double width cards in x16 slots on that board (note two of the 4 x16 slots are next to one another on that board, so both can’t be used with double width cards).
Something like the Asus P6T7 WS SuperComputer board can theoretically take 4 C2050. I have no experience with it, however. You should keep in mind that if your application needs a lot of PCI-e bandwidth, that you won’t be able to achieve full host<->device bandwidth on all cards simultaneously in you are running more than 2 gpus on any Intel X58 board (or any AMD 790/890FX board either).
EDIT: yes the Asus Rampage III Extreme has the correct slot layout for 4 GPUs. Same caveats apply about bandwidth.