Question about be quiet! Dark Rock 3

Here you can find the exact dimensions of the cooler: http://www.bequiet.com/volumes...
Whether your RAM bars are too high depends on the type of your mainboard! So you have to ask the question more precisely!

Which mainboard? Which RAM bars (exact designation).

As long as only 2 bars are used, pretty much any RAM can be installed. I have installed 2*Corsair Vengeance...4 bars will hardly fit down...