That's my whole beef with my own mac - it was one of the last of the batch of PowerPC processor machines before they switched to Intel, and everything I'd ever want to do with the machine has a requirement of it being on the Intel platform. So now the machine is my photo album.
One thing that could be messing with you to make it feel a little different - even if just a slight bit - is that many newer macs with built-in screens have monitors with 100 ppi resolutions, as opposed to the usually-standard 72. I could be messing with what your eyeballs are used to pixeling on. Not sure if this would affect the smoothness/performance of your cursor.