the last agp card I bought was a HIS 4670 iceq version with hdmi output. its not very powerful.. plus whenever I would try to use the HD audio it would get an IRQ conflict and start using up 10-30 cpu% at idle.. I was using an old NF3 based mobo and the bios did not have anything coded to handle more than 1 device on the irq for the video card.. well this agp card has a 2nd buildin audio device, so the bios would try to assign it to a 2nd physical irq (even though the vga was on a diff physcial one.. which in turn caused the processing overhead..
I googled around and found a post from a very intelligent person who goes by the name ARTBIO.. he laid out a procedure to dis assemble the bios into source, modify it to include a 2nd device for the agp irq assignment, re-assemble and then reflash the bios..
Despite my best efforts, I got it to work.. but the limited bandwidth of the agp bus created nasty distortion and squealing noises when pushing video thru it. So after all that, I ended up disabling the hd audio and installed a sound blaster xfi elite pro audio card.. works alot better that way...
Being that the 4670 was one of the last agp cards to be marketed, I would assume that it would also be one of the faster cards used for this slot... (but by todays standards its woefully under powered) they also marketed a pcie version too..
So theres my two cents worth.. HIS 4670 iceq.