Do both cards exhibit the same visual problems? If that's the case, I'd say the monitor is the issue, both cards having the exact same fault seems highly unlikely. Can you pictures of the cards? I'm interested in knowing whether they use the same DAC.

I have some ISA/VLB/PCI cards where the picture will start wobbling after a while on an LCD monitor that I use for testing, yet they work perfectly on a CRT. Others do not display anything at all when using the LCD, as if they were unable to sync. In general I've found that using LCDs with these older cards is kind of a lottery.

I fugred it works with my other monitor. I guess LCD's are just difficult with those old cards...