I would strongly recommend going with scrypt mining rather than SHA256 mining.
Its easier to mine scrypt alt coins than exchange them for LTC or BTC. Works out to be better return than just mining BTC with asics.
E.g. Dogecoin or Earthcoin (now). Mining around millions of coins per day with a $3k GPU mining rig. Easily dump them for $hundreds when it hits exchange. No way you will get those types of return for mining BTC. Especially when 2 ~ 3 THash machines are going to start shipping soon. Your asic will simply get eliminated by the amount of difficulty it will bring.
So would 4 r9 280x be a solid rig? I actually have 3 currently and could easily get another. By the way the CPU is not important, correct?
Also how do you feel about peercoin?
Thanks for all the help.