I agree with jeffrly. If you'll be using applications that allow for cuda acceleration, definitely go for a 680. It will improve speed in supported applications immensely. Also, for a cpu cooler, you may want to check out the NZXT HAVIK 140. Logan reviewed it, and got some ridiculous temps with it. As for the 3770k, you should able to keep it at 4.5 ghz no problem.
Depending on what windows operating system you have can determine how much RAM your computer will recognize, Windows 7 Home Premium 32 bit I believe only recognizes 4gb as the 64 bit only recognizes 16gb. While the 32 bit of Windows 7 Pro. can only recognize 4gb but the 64 bit can recognize 192gb. This is my info source: http://msdn.microsoft.com/en-us/library/aa366778%28VS.85%29.aspx#physical_memory_limits_windows_7