990FXA-UD5 board you might find for 100.00 USD and supports 5 gpus without having to short out the pcie slots.
As for the GPUs I would suggest either MSI R7950s REV 1.0 8pin 6pin (not hardware locked) or Gigalock cards flashed to F43 BIOS or you will be stuck with a hardware locked voltage of 1.250v.
4,000KH/s is not going to get you many LTC these days, you would be better off mining DGC and other ALT coins.
This site is helpful for determining what coins to mine.
http://www.coinwarz.com/
As for the GPUs I would suggest either MSI R7950s REV 1.0 8pin 6pin (not hardware locked) or Gigalock cards flashed to F43 BIOS or you will be stuck with a hardware locked voltage of 1.250v.
4,000KH/s is not going to get you many LTC these days, you would be better off mining DGC and other ALT coins.
This site is helpful for determining what coins to mine.
http://www.coinwarz.com/