I have a few 4.0 installations where I doubled the system memory and added additional PEC cards under the theory that a PC runs faster with more memory.
I just tested again before posting, additional memory makes the boxes far more responsive. I have a couple with more memory and no additional PECs. They are just as fast so the PECs do not seem to have any impact on management speed. The first time I tried this was with an old 1000 where I maxed the memory, upgraded the CPU, replaced the hard drive with a 7200rpm 16meg cache drive, and maxxed out the PECS. That was one seriously fast unit. With all the mods I didn't dare ask my vendor to support it. Too bad.
NARSBARS