To answer your question, they are both integrated graphics level of performance, so it's a toss up. I'd use the 530 if only to save myself from having to install a crappy card.
I had a 5450, which is less powerful than the 6450, and it was a dog in gaming. Even with more stream processors, I bet that 6450 was just as unsuitable. I'm surprised you don't remember the performance level you got out of that 6450.