I had the same question today - found your thread with no answers...
So I did some digging and figured it out. Registered here just to get you the reply 
In the file gajaxscroller.php around Line 109, _animateup is defined:
Code:
// -------------------------------------------------------------------
// _animateup()- Move the two inner divs of the scroller up and in sync
// -------------------------------------------------------------------
gfeedpausescroller.prototype._animateup=function(){
var scrollerinstance=this
if (parseInt(this.hiddendiv.style.top)>(this.visibledivtop+5)){
this.visiblediv.style.top=parseInt(this.visiblediv.style.top)-5+"px"
this.hiddendiv.style.top=parseInt(this.hiddendiv.style.top)-5+"px"
setTimeout(function(){scrollerinstance._animateup()}, 40)
}
else{
this.getinline(this.hiddendiv, this.visiblediv)
this._swapdivs()
setTimeout(function(){scrollerinstance._rotatemessage()}, this.delay)
}
}
The important numbers:
40: Number of milliseconds between movement. The lower the number, the 'smoother' the movement. However be warned, this WILL up the client's CPU usage.
5: Number of pixels to move per movement interval listed above.
So the default setting is to move the text up 5 pixels every 40 milliseconds.
For example, changing 40 to 80 will make the scrolling 'slower', but it will look jittery as it's still moving 5 pixels, just at a slower rate.
Changing 5 to 2 will make the scrolling seem slower as it's only moving 2 pixels every 40ms, but will up the CPU usage.
Finding a happy medium that you like will be up to you.
I'm happy with 40 and 2.
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