superfree are called superfree because they can be eaten on any day. Superfree foods are very very low in calories, and high in water content, so they fill you up whilst taking in very few calories. If you increase your superfree quantities, you are likely to be restricting your portion sizes on the higher calorie foods, therefore taking in less calories overall.
Superspeed and speed foods are supposed to speed up your weight loss, but aren't necessarily free on all the plans (eg, baked beans aren't free on a red day). They are often not particularly low in calories, but are filling and slow-release foods, so keep your body going for longer. Whilst they are good for you, and boost your losses, if there were a superfree food as well you could very easily take in far too many calories to lose weight if you ate them unlimited.
They should give them different names really, as they sound too similar, but have completely different purposes on the plan! __________________