Personally I would split it a bit. With 5k I would throw at least a thousand into buying the currency itself, however you mentioned wanting to invest it all in mining.

You could get a 3x7970 setup for around $1900, although if you decide to go litecoin mine you may want to look into 7950s instead. 3x7950 would cost you around $1700-ish and put out around 1.8MH/s if properly tuned. You could grab three of these for 1700x3 = 5100 and make some great mining proceeds. If you want to buy ASICs, I would go with two BFL singles (50GH/s).

If you are planning to enter into Litecoin mining, keep in mind ASICs will not do this. As well, it will take some good tuning to get your cards to run optimally. Some people on the forums (myself included) sell pre-built miners that come already optimized for you.

If you were to go this route, you could get 4 machines, each with 2 7950s (so, for $60 less, you are talking about missing one 7950 as opposed to making the units yourself), tweaked to reach close to their best potential. That would run you around $5000 as well, assuming you live in the US.