So your PC is slower than a console? I think there are memory leaks and other crap going on, we've tested bikes on minimum hardware and they should keep up with chunk loading under normal rules. Add some mods in or have more than 8 players on a server, or a server that isn't fast enough, and sure there could be problems.
But to answer your question, the old minibike was probably the "top speed" and the new one will be nerfed some so that there is a noticeable upgrade for the motorbike.
Right now we're just hooking up the new stuff. There hasn't been any balance, but nobody has fallen through the world once with the new system, and there are some other very nice surprises I will reveal soon that came with some of the framework changes we made to support real vehicles.