I think the different results you get from BSD/different linux distros are just the result of ending up with different configurations for XF86. As pointed out above, these all use the same code, compiled on with the same compiler, and really just differ in their configuration tools.
If you want to get the best out of your existing hardware I'd suggest reading up as much as possible about what goes in the XF86Config file and adjusting parameters such as resolution, screen depth and monitor sync rates.
If you can find a Knoppix live CD that is a good experimentation tool, as you can set a lot of these things at the boot prompt, and have a look at the config file Knoppix creates.
But if your monitor settings are within specification, it seems most likely bad hardware.