To be quite honest, I've done so many things to my phone since I got it (save of bricking it) that I didn't pay attention to any difference in performance of apps used in the SD opposed to having them on the phone.
For me, the most important thing, is the fact that I save space on the phone's internal memory, which in my case is really low. I can always delete songs on my SD or, if things get that far, buy a bigger SD; can't really do that with the phone.