Just a word of warning in your search for a graphics card.
You mention an Opalvision - I've been reading that Opalvisions are not RTG cards and will not give you a high-res, true color Workbench. It only works with apps designed to use it, like a handful of paint and presentation programs. Its use seems to be extremely limited.
If you are wanting a nice high-res Workbench, don't look for an Opal or you could be disappointed. CyberVision or Picasso series are your best bets. :-)
Anyone please correct me if I'm wrong. I'm going by TBBOAH (
http://www.amiga-hardware.com/showhardware.cgi?HARDID=485) and an eBay auction I saw a while ago for an Opal. The seller (very honestly, unlike a lot of the Amiga eBay conmen) mentioned this.