I have tried to switch to Full Stop option from Constant Velocity and cant quite understand how it works. The whole feed began to slow down, jumping up and down with considerable finish degradation. What is the point in full stop option? Also there are two CV options under settings screen. What do those do?

Have a look at this doc,   http://www.machsupport.com/docs/Mach3_CVSettings_v2.pdf

Greg