SheepShaver was originally virtualised and not emulated. The original version ran MacOS in a virtual machine on PowerPC BeOS (BeBox and Mac that ran BeOS.) Because of this it ran at full speed and was akin to the Classic environment on early MacOS X. I used to use it to run IE5 as the BeOS browser was quite poor and PowerPC never got any ports of more modern browsers. It ran really well and could be made full screen.