I have one 280x in one of my systems and I'm getting about 720kh/sec with minimal tweaking.  I'm sure I could get a little more.  It's very solid, good choice. 

I think the ASICs will be awhile, nothing concrete yet.  You can always sell the hardware later to gamers, which minimizes your risk.  And, it's a bit of fun. 

Middlecoin is a good choice, I use them and like them.  With a limited hash rate, you can probably do a little better by watching the coins (coinwarz, coinmarketcap, etc), mining when diff is low, selling when value is high.  More work, a little higher risk, but more rewards, if you have the time.

Good luck!