I have done a rather in depth comparison of loading times in MSC. The compared versions include both a PAL and NTSC version running normally on a Wii. A PAL Wii U version. And finally a PAL version running on USBLoaderGX on a Wii. Take a look:

The results are quite surprising and should result in an immediate change in the rules based on the conclusion. USB Loader GX and even other loaders (after they have been tested) should be allowed for these runs as they make the loading times most similar between the Wii and the Wii U. Otherwise the Wii (the console the game is made for) is at a disadvantage. And banning the Wii U would not be a good idea. Most people nowadays have a homebrewed Wii as it is very easy to set up, so allowing USB loaders should be the perfect solution.