Ghz, ignore it. CPU wise, AMD if you're poor, Intel if you're not. Intel is much more stable.

RAM, you need at least 8Gb, 16Gb or more will help in a big way. I use 32Gb. 16Gb is rapidly becoming the new minimum.

GPU, it's all that really matters. They don't sell PC's with good GPU's and shitty CPU's, which is why I say ignore the CPU.

On GPU's...

Intel - cheap shit. It will run games, but you wont like it.

AMD and Nvidia, they are the leaders. Steer clear of AMD, they have massive driver issues that have been going on for many years now, they're almost sorted, but almost isn't good enough.

Nvidia - pretty simple. 3 numbers. First number is generation, last two numbers is where it sits.

For example, a 780 is the top of the line card of the previous generation. Will run anything at max detail flawlessly. Same can be said of a 980 (current bleeding edge) or even a 680 (getting a bit old now, but still kickarse).

750 will run most things at max detail pretty well. It's not perfect, but it's a very good value option. Anything lower than an x50 is poo.

Then there are the x90's. For example the 690, 790, and 990. They are actually two x80's on one board. Ultra expensive, and a bit of trouble (not all games can use more than one GPU). But if you know what you're doing, awesome.

In short, look for a 650 or 750 if you're looking to save money. Get a 980 if you're not.

Lastly, laptops have the "M" models. A 980m is about 90% of a 980.

Also, Nvidia put's an X in the name to let you know its high end. For example, it's the GT750, or the GTX780. X's make everything better. There is no GT780, all 780's are GTX's.

Nvidia also sells it's "Titan" range of GPU's. Simply put, you can't afford them. You don't want one either, they're really for Scientific computing.

Lstly there are the "Quadro" cards. These are not for gaming, they're for CAD. They're over double the price, and are actually slower for games.