What is more important CPU or RAM for compiling large software, e.g. bootstrapping gcc?

I'm looking to buy a new computer soon, and I want a machine for best performance for fast compilation times.

So should I care to get a quad-core CPU with highest GHz I can afford, or should I instead invest into higher speed RAM?

What is your recommendation for what type of RAM should I go for?

Graphics performance doesn't matter, compiling loads of software & running mathematical simulations.

I would say neither. Rather get a fast SSD hard drive. Of course you need a proper CPU and amount of RAM as well, but yeah...

Probably RAM will give you a bigger bang for the buck. Compiling, especially large applications, is very I/O intensive, and having more RAM means you can save more time paging to and from disk. Most CPUs today, especially if you go with a cheap quad-core, will provide plenty of CPU power for your compiling, but having the RAM will help with the data going back and forth.

On 2nd thought, it sort of depends on your math simulations and build processes. Are they parallelizable? If not, adding more cores won't really do anything to speed it up, although the new Intel chips (Core i7) are quite fast on a per-core basis.

I'd say get loads and loads of RAM and use ramdisks for temporary storage. This will dramatically increase speed of compilation. A fast multi-core CPU would be fine too, but I think that you'd benefit more from lots of ram. Take a look at this article for some ideas. Here's some more information and some more here. I think that using RAM will be faster than using SSD, but I could be wrong.

For your computations, your processor is by far most important.

The compilation will stress both your processor and RAM.

I think your most cost effective solution would be to get the best CPU you can afford, and preferably a Quad core. With RAM being as cheap as it is (DDR3 is now as cheap as DDR2), you can easily plug in as much RAM as you need for little coin (16 GB of DDR3 for $180 on newegg ... I realize that is overkill, just trying to demonstrate how cheap it is). So I would invest as much as I can afford on a quality CPU as possible.