I recently got some TwinMos ram from the MM which has heatsinks. I personaly am not in a great favor of these purely because if I touch the ram stick after the PC has been under stress for a while, they feel very hot to the touch, while the ram sticks which aren't covered with such a heat spreader, feel a lot cooler.
So to me personaly having such "heatsinks" is just a faster way of destroying your ram rather than improving performance on them, unless ofcourse you have a 120mm fan right above the ram cooling them maybe ;\