5GB is too light on memory, means that you still have two older original OEM FBDIMMs that are not contributing much other than heat and using 10W each.
Pull those, get a set of 2 x 2GB $25 (or less) on Amazon, throw in a 250GB ($139) SSD and your system will be much more responsive.
You have 64-bit processor but 32-bit EFI so as is you are not using 64-bit kernel and drivers and apps are "limited" to 3.5GB per process/task address space - not usually a huge issue and seeing you only had 5GB anyway you would not have seen or used more memory per processor to see an improvement.
New FBDIMMs even when they are not Apple approved with heat sinks tend to run so much cooler anyway and some users are using standard server grade FBDIMMs - not that you need to given the cost and availability of those that do on Amazon "Mac Pro FBDIMM 667MHz"