Overall Shooting: Nikon D600, D800 or Sony A99

I'd choose the D600, it seems to be have slightly better ISO handling than the D800, is $1k cheaper than D800, and is slightly faster fps for shooting action.  I'm not too sure about the Sony, but if your happy with your D300 and you already have lenses, I highly doubt the Sony A99 will be so much better to justify the higher cost plus all new lenses, flashes, etc.  I just upgraded from a D7000 to a D600 this past friday.  ISO 6400 sooc look FANTASTIC, even iso 8063 (hi0.3) looked good enough for simple family shots or grimy b&w's!  Also, being that you shoot many different styles, you'll take advantage of the U1 and U2 settings on the D600 that are not featured on the D800.

ISO is better on D600 at 1:1 pixel level but downsize a 36MP image to 24MP or below and D800 is ahead from everything I have seen... worth a check out.

If you have any DX lenses they're very functional on a D800 too at 15MP. AF on the D600 is using D7000 AF system (a DX system) on an FX frame - I understand its compact in your frame so not as useful for tracking/auto AF functions. D800 in DX gives you a near complete frame of AF points! D300s AF is superior to D7000, you may feel like your taking a step back in everything other than sensor. Your D300s has very high FPS rate, neither the D600 nor the D800 can compete or are going to replace that body for it. 

Layout of the D800 is closer to your D300s than the D600 - the ISO placement on the D600/D7000 on the back buttons is horrible (for my preferences), though the D600 has improved with putting it on the bottom button by the LCD. 

D300s is a perfect second body for fast action or a dual weid with e.g. a tele and a D800 for those slower moments. Might need some more CF cards though. As a D7000 to D800 mover I think you may feel like you're missing out with a D600 more than I would have given the D300s is a superior unit to use than the D7000 (not talking sensor/IQ here, rather about 'getting the image'). Consider your workflow implications of having 50MB+ raw files from a D800 as at least with my computer, things are much slower than the 20MB D7000 raws. You'll be happy with either but if you have the money for the body and FX lenses why not step it up all the way?

best all around camera and with the current price drop, the most affordable.  Switched to Nikon from Canon for this camera.

You can always have a 1.5x crop factor with 15mpx resolution which mimics your d300s, and you get a pro level dslr vs. enthusiast dslr.  I have d7000 and d700 and it's night and day in handling and options...and I kind of have a feeling that d600 and d800 have similar differences (except that both are fx) when options and feel is considered.  I have no experience with a99, so I cannot comment.