64MB cache, 6GB, 10000R, which one is most significant?

[klein_orz]

I want to build my first DIY'ed computer system via OcUK, however, I am kinda struggled with this question: which one of these is most significant in improving speed, 64MB cache, 6GB transfer rate, or 10000R HD?

I may probably go for a 950 system with either 1600 or 2000 memory, I just do not want my HD be a bottleneck for my scientific computing and furthermore, I don't have the budget to buy a SSD...

Thanks!