I Think the FG of this airplane is crapy.
The A/THR soft mode allows a variation of +- 3 kts , when in ALT CRZ and above M.65.
The point is , sometimes you are already 10kts above or below your target when the A/THR slooooooly starts to adjust, That`s why pilots have to intervene , selecting mach and sometimes changing to IAS.
By the way , the same poor behavior hapens during descent specially in the 300 series. Speed goes sometimes 10 kts above the bracket and takes times to reduce by itself.
Not to mention the calculation of the descent profile. If we are high on profile , it shows the intercepting point , and then as we get closer it moves ahead over and over again; it was suposed to be at 250kts at Fl 100 and it does not reduce , or starts reducing well before and all of sudden you find yourself at 250 kts at level 130 , etc....
My company planes are equiped with Thales...
The A320 is a loooottttt better than the A330.