I will clarify some things. :-D
1. Single Board Computers DO NOT bind with the amiga. with a goldengate u use the amiga keyboard/mouse/HD/serial/parallel/floppy drive/ram etc... so if u just stick there a SBC u will neet it to have it's own HD/CD/keyboard/mouse
2. the 486slc/25mhz perfoms a little more than a 386DX/40mhz. it is a drop-in replacement for 386 chips, and it has some internal optimizing. the ideal would be a goldengate 486slc/50mhz :-D :-D
3. even with the gg486slc u will need to find a good sound card and vga. all soundcards work, but some are buggy with the GG486. I have found that NON-PNP ESS1868 based ones work perfect, and I have tried lots of cards.