I don't want a flame war but the whole point about simulators is that they might run at nothing like the same speed as a real system either lots faster or lots slower but you can still accuratly model a system because in the s51 simualtor for example you can set the baud rate of the simulated transmitter connected to the 8052 and you still get an accurate idea of what happens when you send data at that baud rate on a real system.Its the same as me using modelsim to simulate a fpga it runs a hell of a lot slower then the real thing but you can still see what happens in real life.
As for using DOS all I can say is ive used both the DOS and unix versions, they work, the DOS version if anything has a beter interface than the unix one.I am not a great fan of DOS but it does the job sometimes.