Here's the thing. When your phone uses (you use) the app, it has to be in memory. That's the memory that is most like the memory in a desktop computer. We'll call that working memory, and in phones there's not very much of it. Because it doesn't have a hard drive, your phone stores things that it's not using in either a different kind of memory or on the SD card -- like you'd store programs and files on the hard drive of your computer.
Moving an app to the SD card frees up the storage memory of the phone, but it really shouldn't have an effect on what happens when you use the app.
The Android operating system manages the working memory, keeping it full of apps you're using and apps that you're not using but that Android thinks you will use soon. If android has guessed wrong and you attempt to use an app that isn't already in working memory, it will kick out apps that you aren't using until it has room for the new app.
Android does pretty well at managing working memory. That's why task killers usually don't do much good.
If your phone is slowing down, either the app you've just loaded is behaving badly or some other app in working memory is behaving badly. If you get the "out of memory" message, you'll need to start clearing caches and maybe you'll free up enough memory to speed things back up.
But if WWF is the only app that slows down the phone, I'd bet on a problem with that program, and moving WWF to SD won't cure it.
I've really oversimplified here and done some damage to the finer points of memory management under Android, but I hope it will give you an idea of the problem.