I found the Pearl/Diamond games kind of slow. For one thing, there are a few delays. For example, battles with AI characters. An AI character notices you, then, after a few seconds of standing there doing nothing, they decide to come over to battle you. The response was immediate in other generations, so what's with the delay here?
I've also noticed slight delays between attacks in battles that weren't in other generations, but they could be loading times...
Of course, all generations had speed-related problems. In Red and Blue, you had to manually go into the items menu every time you wanted to ride the Bicycle. The second-generation games fixed this problem by allowing you to register an item to the Select button, but still, both this generation and the first generation didn't give you the ability to run when you wanted. I found that the third generation's main problem was how long it took to start every battle (this was mostly a problem in R/S/E... the pre-battle animations were a lot shorter in FR and LG). Pearl and Diamond have delays here and there, the saving times are long (especially when the game is saving "a lot of data"), and the walking speed is just painfully slow.
I have yet to experience Surfing in the Pearl version, but from the sounds of it, it seems like it's going to be somewhat torturous.