When an application needs more RAM, than available, it uses the hard disc as additional RAM, but this is slower. So, more RAM speeds up the computer.
The GHz says, how fast the processor is. Well, not really, but in a family of processors it says much.
I don't know about today's processors, but in the time of Power PC with Mac OS only and Pentium with Windows only, they tested the influence of processor clock to the speed. Twice clock means, the speed is about 50 % faster.
Funny thing, that a Power PC with 500 MHz with Mac OS X was faster, than a Pentium with 1 GHz.
The manufacturers made the speed faster and faster, till you would need an own nulear power station. One time they turned back the clock speed and made the processors faster.
So the latest intel with 1,4 GHz are faster, than old ones from 2002 with 2 GHz.