In order to get perfect scrolling in (PAL) Amiga games, your display must run with a refresh rate of 50Hz (*) and you must have video synchronization enabled in FS-UAE.
Video synchronization will automatically be enabled if FS-UAE detects that your display runs at 50Hz and you have enabled video sync in preferences. In case it doesn’t detect it, you can force full video sync with the video_sync option. If you force this, and the display isn’t running at 50Hz, the emulation will instead run at incorrect speed and you will get issues with sound.
(*) When running NTSC Amiga emulation, your display must be running at 60Hz.
Enabling 50Hz Modes
Depending on your system and display, this can be either easy or difficult to get 50Hz modes working. If you have have a 1920×1080 monitor which announces it’s support for 50hz properly, it can be as easy as just switching the refresh rate with the control panel on your system.
In other cases you may be able to create a custom 50Hz mode for your monitor. For Linux, you can tweak modelines in Xorg.conf, and for Mac OS X, you can use a tool such as SwitchResX.
Windows users may be able to use a program called Powerstrip to create a 50Hz mode for the monitor – if a 50Hz mode is not already available.
50Hz Modes in Linux with nVIDIA
With LCDs and nVIDIA drivers, getting a working 50Hz mode can be a bit difficult in some cases, so I have written a how-to on 50Hz display modes on linux with nVIDIA drivers.