24-70 CZ vs 16-50 SSM, A99 vs A77?

It might depend on what subjects you like to shoot.  I'm more of a portrait/landscape guy.  I almost never shoot handheld in low light or action shots.  In your position, I would go FF, which is what I did with the 24-70CZ, and I couldn't be happier.

I don't own a NEX-7 (but I've seriously looked at one), but I don't think the a77 would be a big step from that.  If I'm going to drop the money on a new body, I want it to do something for me much better than my current one.  This is part of the reason I'm not interested in replacing my a850 with an a99.  If the a99 had the D800 sensor in it, I'd be very interested.

So, you need to figure out what your limitations are, and what camera best overcomes those.  I would consider going with the a99 and starting out with the Tamron 28-75.  Then, you can trade up to the 24-70CZ at some point.

Please note, all of my comments are based on using the cameras for still shots.  I'm not considering video, as it's not something I look for nor have in a still camera.  Good luck with your decision.

--
yakkosmurf
http://www.flickr.com/photos/yakkosmurf/
a850, a700, R1
24-70CZ, 16-35 CZ, 135CZ, 70-400G, 70-300G, 16-80CZ, Sig 24 1.8 & 10-20 4.5
F58AM flash