would 8gb of ram be enough for photoshop and video editing??
if i buy 16gb should i buy 2x 8gb modules that are not together in the package but the same brand(because it would be cheaper)??
or buy 4x4 that would be in the same package??
8GB should be a very comfortable amount of RAM for Photoshop and video editing.
If you're doing that type of work for a living - making money - I think you might want to get the 16GB. Choosing a matched set is always best.
It would be 'better' - but not 'much better'. I don't believe you'd notice the difference.
You shouldn't let yourself be scared of the 3570K running hotter.
It's OK at 4.5Ghz - which is about the same as i5-2500K at 4.8Ghz.
8GB is more than enough for Photoshop/Video editing. Make sure all your RAM modules are the same and use CPU Z software to check at what speeds the RAM is running. Many times, RAM underclocks itself due to the Intel chip. This can be easily fixed by going in the bios and selecting XMP profile from the overclock screen. Note that this isnt considered overclock if your RAM is rated for that bandwidth and forcing it to run at its bandwidth won't void warranty.