WZC wasn't the fastest besides space if memory serves... Put it on ground, and the thing flaps around like a lame duck (or it's supposed to anyway, you can get sustained flight for about 5 minutes I think I read somewhere? But hovering/walking are nigh impossible...)
Deathscythe and Sandrock are the fastest on ground. Nataku is kinda slow, which is odd considering how it's also close range only, but I think they offset that via the claws as a sort of "Scorpion" effect (GET OVER HERE!!!!). Then Heavy Arms I don't believe they have a speed really listed as it has never been used for speed... It's just known it has the greatest length strength to weight ratio of all mobile suits, as it is capable of jumping higher and doing more with those acrobatics than any other suit...
Otherwise, they made the one fatal flaw that many games are making nowadays... Everything is too close to everything else... A Zaku II can be about as good as Nu Gundam. The only difference is attack style. Sure there are still stat differences, but they are far too minor T.T
TW SDGO: Ferox