A HDD will bottleneck a new system with 8GB of RAM. 1G of RAM will bottleneck a new system with HDD.
It is all about getting the right balance. If the CPU needs the information, it asks the RAM for the information. If the RAM does not have it, then the RAM asks the HDD. With a SSD you cut down the times that it takes to get information that is not in the RAM. It makes your entire system seem snappier.
I would not bother getting more than 8GB of RAM for a gaming machine.
Ignore RAM drives, despite the awesomeness of one, I doubt you will ever use one.