Dual/quad channel capability is determined by the motherboard.
For most, like socket 1155, there is dual channel only, regardless if populated by 2 or 4 sticks.
You would do better with 16gb in a 2 x 8gb configuration. It is usually cheaper, and two sticks are easier for a motherboard to handle if you are overclocking.
1.5v ram does not need any heat sinks at all. They are mostly marketing. Tall heat spreaders can interfere with some cpu coolers. Only if you are a record seeking overclocker trying to reach maximum ram speeds might there be a benefit.
And... high speed ram may not increase your fps or app performance to be worth much.
Read this: http://www.anandtech.com/show/4503/sandy-bridge-memory-scaling-choosing-the-best-ddr3
Lastly, ram vendors will not support ram from different kits. If you add another 8gb , you are on your own if it does not work properly.