I'm sorry for that, my settings don't work on your machine, or you can try edit 2FScrollAccelMode and ScrollSmoothSamples values yourself
located at IOKitPersonalities-> Smart-Pad-> Preferences-> Scrolling on the info.plist.
I just modified info.plist to fix slow scrolling with the trackpad, I have tested it on my ASUS K401LB and everything is back to normal now.
If you want to try, I attach this kext below.
ApplePS2SmartTouchPad v4.7 beta 5.zip