Hi;

Right now I'm running Carrara 8 pro (64-bit) on my main machine, which has 4gb of RAM.  As well, I use a render node on two other machine, which also have 4gb of RAM.  I was wondering; if I upgrade my main machine to 8gb of RAM, will my render nodes be able to render scenes that, when open on my main machine, use between 4gb and 8gb of RAM?

 You can never have too much RAM. However, you don't need to upgrade the nodes. The only issue really is if you are rendering scenes that actually use the full complement of RAM. If you do, then the nodes with less RAM will start writing to disk and slowing the  process down, canceling speed gains that the main machine would normally have. 

I agree with Mark.  I personally wouldn't do any complex scenes with less than 8GB, which is what my main box and two node boxes all have.  The difference can be pretty noticeable.  Not to mention that 8GB will speed up a lot of apps that have high memory usage, not just Carrara.  With RAM as cheap as it is now, it might be worth considering an upgrade.

Yep, ram is cheep right now. I just picked up another 4gb for $80 for my other quad. So now all my PC's have a min of 8gb. That's Cnd$ we tend to pay more for parts than everyone else.