The heater core acts as an extra heat exhanger, there is no question about this.

10 times out of 10 every car I see with no heater core runs hotter than cars with heater cores. I have plenty of datalogs to substantiate this claim. You can get away without one sometimes, but in a car that is drive on the street, you are better off with one. All the fans in the world won't help if you cant dissipate the heat in the coolant. Weather you are willing to tolerate the higher temps is up to you. With how sensitive most DSMs are to HG issues, I would keep it as cool as possible, within reason.

220 is pretty hot there. I always try to keep my cars running around 185ish when beating on them.