nah cs 5 has content aware feature which kinda automates patch tool and allows you to fill a certain area based on its surroundings. that's one of the coolest new features
You can use either of them , CS5 is the latest version of the Photoshop with advance feature and templates. If you are good CS4 than you can automatically switch to cs5 with no problem
CA4 and CS5 have the same specs.. there were some tweaks that where needed to run the program smoothly. But all in all there is not difference.
CS5 is essay because it is new version and have better and more quality then CS4 so I would like to recomend you CS5.