Also I compared both the 550 ti and the 650 and isnt the 550 more powerful?
Very slightly, if your case. The 550 Ti will be enough. The 650 will play newer games a little better than the 550 Ti due to its newer architecture. But the games you're playing are mostly CPU dependent. Not saying they dont require a good GPU, but the 550 Ti would do just fine for what you're wanting to do. But if you can get the 650 or the 650 Ti at the same price or close to a 550 Ti then definitely pick that up.