In the US the 412s is about double the price. Only difference I can see is that the 412S has been plated, so I assume it has a near mirror finish on the bottom.
Evo 212 is a decent cooler, not the best on noise or cooling, but just about the best price/performance ratio out there. There are several equivalents but which is the best to pick depends on what sales are going on.
You do have to worry about maximum height, some cases are two narrow/short to have these stuck on.
Xigmatek Gaia, Thermaltake Frio, and a few others.
While the CPU is the primary factor to overclocking,the motherboard is just as important. Depending on the quality of the VRMs and their ability to maintain a proper voltage despite rising temperatures may be the difference between running stable at 4.5Ghz or having to drop down a little to gain stability.