An interesting suggestion came for comparing the RAM & CPU usage of the four Linux sisters: Ubuntu 12.04 LTS, Kubuntu 12.04 LTS, Xubuntu 12.04 LTS & Lubuntu 12.04 LTS.
As mentioned in my previous post, Ubuntu seemed to be the most taxing on CPU & RAM whereas Lubuntu seemed to be the least. The same results are validated when I booted each of them from pen drive and checked the RAM & CPU usage.