> I have no idea if AmigaOS 4 can or cannot boot with
> its graphics card in a non-primary slot

IIRC from the discussions over the years, if there're two OS4-compatible graphics cards installed in the X5000, OS4 will always use the one in the primary slot. There's no way to make OS4 ignore the card in the X5000's primary slot and use the (better supported) one in the secondary slot instead (or in addition). This was stated as an unfortunate regression from the X1000 where OS4 can even use two graphics cards concurrently in a dual-GPU setup. I have no idea though about OS4-incompatible graphics cards in the X5000's primary slot as all MorphOS-compatible graphics cards are also OS4-compatible to the extent that OS4 can boot with them.

> MorphOS [...] couldn't boot at all with a Radeon in anything
> but the primary (x16) slot. At all. It wouldn't even get to
> the point where it would try to load the Radeon driver.

Thanks for the clarification. Do I understand the situation right that pre-3.17, MorphOS couldn't even boot with a MorphOS-compatible card in the X5000's primary slot as long as another Radeon (MorphOS-compatible or not) was inserted into the secondary slot?