you should get 6000kh with 6x r9 290x cards I will look into it for you but honestly 4btc is far to much to pay out for that info as its is available on the forum for free


Edit a r9 290x is meant to get around 900kh-950kh if overclocked so 6 will get you around what your aiming for I would advise you to make 2  3 or 4 card rigs instead as they will run much cooler and you will have less issues

the other option is to go for scrypt asic or fpga but there not readily available at this time