I think that PC-Engine can be emulated well with an 030/50Mhz using my own emulation system (I use 100% assembler and AGA hardware directly to make possible to gain A LOT of speed and performance) The only problem is that PC-Engine is capable to show more than 256 color in screen (Tiles + Sprites) But probably few games uses it.
You can test emulation speed testing Parodius Da! in AmiPC-Engine. You cannot play, but the menus and music works!!!!
A PC-Engine emulator coded in C or using AmigaOS will probably require a 060/50Mhz or more :S
My AmiPC-Engine emulator is based on AmiNES, for this reason I developed an alpha version in only two weeks!!! (I left AmiNES develop because other two NES emulators were in development too, CoolNESs and A/NES)
I have in mind to continue AmiPC-Engine when I finish a MSX2 game that is in development now... My friend ZENER (Tracker Hero coder) always is remembering that I need finish AmiPC-Engine
I like Parodius Da! of PC-Engine a lot and all Konami games in general...