GPU first. It'll affect performance way more than SSDs. A GPU controls how fast your games run, and how much graphics it can process. I'd go with the MSI Twin Frozr II OC 7850 or the ASUS (Gigabyte if there's nothing else). Ranking:
1. MSI Twin Frozr II OC
5. Another manufacturer... if worst comes to worst
Try getting more than one fan. Two is the most common.
An SSD only controls data input/output... so it'll speed up your startup time and loading times for games, but actual fps will barely be altered. Make sure your computer can be upgraded! A lot of computers don't have the capacity to be upgraded! You will see a MASSIVE difference in between the 6770 and the 7850. All games should run on maximum settings.
Also, of course, SSD prices are still coming down.