Heatsink has never been removed since I built it. And the ventilation isn't as good, but here's an odd thing. I opened up the side and blew a desk fan into the side of the case at full power and the temps only dropped 3-4 C. When I touched the
HSF after it had been running Memtest (I hadn't installed windows yet), it wasn't uncomfortably hot. I had no trouble holding my finger against it.