g, are you aware that you don't need the silly speeds?
You can smoothly go between values by using the \xx command instead of Zxx.
Even if you use a speed of 80bpm, you can easilly archieve smooth slides.
Basically, when using the \xx, the command will ensure that it was slided to that value at the end of that tick (row). If you use the interpolate effects command, you can get very good slides.
You enter a \00 at one place and a \7z a few rows down. You make a selection, right-click -> interpolate effect and voila! Change the first \00 to a Z00 to have the best effect.