I need to upgrade my camera

If those are FX compatible lenses, I see no reason why not buy the D600. You can't go wrong with it. Also used D700 could be a good choice.

Just saying D7000 as it's a natural step up from a D70 and ideal for an experienced photographer. Lots of control as with the D600. 

The great thing with it, judging by your lenses, is you need a fast prime. You can get a 50mm f/1.8 AF-D for $100 (D7k has motor) if you've not got another $100 spare to get the new AF-S one or the 35mm f/1.8 DX. There's your night life lens. Your current f/3.5 at night is dark.

D6000 - is that a thought for you? It's very expensive - a D7000 with a 35mm sensor that won't be of much use to your DX lens (ok, it's a little more than a D7k but it's not a new breed altogether). D7000 will save you $1000 at least - use to get a decent fast lens. Factor in that a D600 with your lenses will lack a wide end, so with a D7k you won't have to spend $500 plus on getting something to fill that void. So, you're talking about $1500 saving... roughly the cost of the 18-55mm f/2.8 or 24-70mm f/2.8 Nikon pro lenses. :D Sweet. Amazing quality. Quite likely better quality from one of those lenses on a D7k than your Sigma or low cost wide FX lens on a D600.

i recommend sony a57 ... i am use it right now, this camera so fantastic =)