The HD 7770 can play some games at high, but it depends on what resolution you will be playing at. Click below link for some benchmarks. The CPU used is an Intel Core i7-3770K @ 4.7 GHz. All games are using the highest graphic quality possible.
First of all, your resolution is rather low, so ultra might not be possible, but high should look almost the same as ultra if the monitor is small and resolution is under 1650x1080p.
Is it a 21 inch monitor?
Your computer will be definitly slow by "enthusiasts standards" and in the most demanding game it wont probably be able to run over medium settings (thou those titles are not too many).
If you want to OC the CPU, you should get a version of the intel that has a -K at its name. This is how they specify easy to overclock CPUs.
Your GPU... its a bit on the weak side. Creossfire X is not something id recommend due to how many issues you are going to be running into (Not all games use it, drivers are normally more buggy than regular onces, a lot of heat generated, many heat realted problems, micro stuttering, aditional power draw... i think thats about all of them).
If you can get 1 stronger card than 2 weaker (that in total will be slightly faster), you will skip all those issues.
For example you could go for the cheapest 7850 you can find...
As for the CPU, i use a laptop version cpu 2430M and it deal well with everything including stracraft 2 (a CPU intensive game, few are this intensive). YOur CPU will be probably even better since its a desktop version, and if you look at all the benchmarks out there:
CPU will make a diference but in games where FPS actually is in the 20-30 limit, mostly its the CPU that makes a diference.
Personally, once i ger over 40 FPS i can barely tell the difference unless i switch it VERY fast.
Its more important to have a steady FPS, but that depends on the Game coding a lot more than on the hardware so we are out of luck.
One final thing:
Note that creossifre X does NOT add up the ram of both cards. This emans you are still going to have 1GB of ram once you add your second card (and they must be the same model or there is a chance they simply wont work togheter).