The 68000 didn't have virtual memory so can't be compared with the (later) 80386. The 68010 (which I programmed on in the 80s in a Torch XXX) had virtual memory and was the 'mainframe on a chip'.
Also I question this idea of IBM considering the 68000 for the IBM PC. The 68k had a 16-bit data bus so would have meant a more expensive mainboard design than the (8-bit bus) 8088. The Motorola chip to compare with the 8088 is the 68008 (Sinclair QL anybody?).