|I do not know the Redeon cards well, but per the article, the HD 7770 is better than the HD 7750 and nearly the same price in the USA. I do not know what it is by you, but look into it. With gaming, it is generally recommended to go with the best you can afford, as long as your power supply can support it.|
Consider upgrading the power supply to a better one, if not now, then as soon as you can. A cheap power supply can go without warning and take expensive components with it.
You have to be a little bit crazy to keep you from going insane.