A trick I used to do was to jump up to the NTSC equivalent (640x400) which was flickering less in my standard monitor.
In OCS Amiga, Low/High/SuperHigh are defined by the base (as in not using overscan) Horizontal resolution, 320/640/1280.
PAL and NTSC are 256 and 200 lines base vertical resolution respectively, and 50/60Hz vertical refresh rate respectively.
512 and 400 lines are Interlaced modes. The flickering has to do with the interlacing. The improvement perceived with the NTSC mode is due to the increased vertical refresh rate.
ECS Amiga (A500+/A600/A3000) introduces the so-called Productivity modes, which are just the 512/400 lines hires modes but in Progressive, thus doubling the horizontal refresh rate to ~31KHz, while also doubling the DMA bandwidth required.
At full DMA you can form a a palette of 2^2 colors instead of the usual hires 2^4, and unless you have FAST RAM you'll want to keep it at 2 color in order to let the CPU use the odd ram access cycles.
This palette can of course be changed during horizontal blanking, as then the display DMAs are off and the copper has room to access the palette registers, or several times midline if only using 2 colors.
In Productivity mode, as the chip that does actually encode the video receives the same bitrate as usual, the color depth is reduced to 2 bits per channel (from 4) for a choice of 64 colors.
These restrictions do not apply to AGA (A1200, A4000, CD32) Amiga, which are a different beast.
To display the picture from an Amiga today, I do use and recommend the OSSC (Open Source Scan Converter) and a modern monitor with HDMI input.
There are restrictions on some aspects of overscan display, however. They vary between generations of Amiga chipset. e.g. It might not be possible to display sprites outside of a certain area, or display them at all if overscan is large enough.