Hi Chris,
I know other people have experienced different things in the past, but I have always found letting Win7 OS mange the memory by selecting the “System Managed Size” option as being the most reliable in Windows 7. This wasn’t always the case back in WinXP x64 OS days.
Mike
From my experience, this is the most reliable thing to do.
We started with a Vista farm and sometime the best fix for issues there was to allocate a size. But almost every node started giving us issues as we upgraded, and letting the system manage the memory has allowed us to scale far better when we have jobs that are all ram.
If you want your farm to be faster, you should investigate faster HDD or SSD options.
In most cases, this is where your slowdowns will happen.
Barring that, you should run some tests to see exactly where your bottlenecks are and address them first.