I really wouldn't go that far - I actually HAVE a Marshall half-stack, and you just don't get the same feeling as you do when there's actually a 4x12 involved. The tone just isn't the same either. You just can't emulate an actual 4x12 cabinet. You can EQ a thick tone, but it isn't going to make a combo, or even a 2x12 sound like a 4x12.
I was playing it through a 4x12, just not with a marshall head. No, the tone isn't going to be the same, that was my point. Once the honey moon was over I sold it.