Ripjaws, Ripjaws X, Sniper, Corsair,Dominator?!

The difference is marketing.

1.5v ram does not need any heat sink at all. If you are a record seeking competitive overclocker, then perhaps some ram cooling is in order. But not for any rational use. If you have a favorite vendor and like their support, buy from them.

Otherwise same-o same-o.

It does seem like they try to make the heatsinks attractive to the point of by the fact that they look so awsome that they have to be great cooling and fantastic performing ram sticks. Take off the fancy heatsinks and what you have are the memory chips and thier voltage , timings , latency and speed. I do think I answered a similar question and the sweet spot seems to be ;
DDR3 1600 (PC3 12800)
Timing 9-9-9-24
Cas Latency 9
You can get higher speed ram 1866, 2000 , 2133 and it seems like the higher you go the more chances you will have problems installing it and getting it to work with your cpu and motherboard. Thats why I said that the sweet spot seems to be just to be able to put it in and fire it up. It is a good idea to look at the QVL of the MB before you but memory just to check and see what they support. It is not a comprehensive list as I have on ocasion put in ram that was not on the QVL.

On the Sandy Bridge - I agree with @geofelt for Gaming; the differences between DDR3-1600 and DDR3-2133 are 0FPS~3FPS depending upon the benchmarks you look at. My preference is DDR3-1600 CAS 8/9 with 2x4GB density on a 64-bit OS.

The Sandy Bridge unfortunately lack the ability to raise their BCLK >107MHz~108MHz whereas the LGA 1366 and seemingly the LGA 2011 don't suffer this limitation so if history repeats itself then I suspect you'll see again the LGA 2011 show improvements with higher Frequency when combined with higher BCLK. So I hope to see 2FPS~8FPS+ when OC'ed...

As far as temperatures, it depends on Frequency and in particular Voltage. The 1.50v sets aren't goinf to get hot, but the 1.65v or higher do get hot. Ideally, the Sandy Bridge it's best to stick with 1.50v and maybe 1.60v at DDR3-1866 or higher Frequency.

The differences are some RAM IC's are indeed better then others. For example the G.SKILL F3-12800CL9D-8GBXL work fine at their rated DDR3-1600 CAS 9 in 2x4GB, but often they run DDR3-1333 in 4x4GB (2 sets). So I recommend the G.SKILL F3-12800CL8D-8GBXM DDR3-1600 CAS 8 which will run DDR3-1600 in 4x4GB (2 sets).

Next, OC'ing the RAM some will exceed their Rated Frequency and CAS, and some will not e.g. Corsair Vengeance.

Articles:
Tom's - http://www.tomshardware.com/reviews/corsair-vengeance-c...
Bit-Tech - http://www.bit-tech.net/hardware/memory/2011/01/11/the-...

Tom's4GB ~ 16GB - http://www.tomshardware.com/reviews/ram-memory-upgrade,...