I don't know exactly how LiveCD works, but I know that everything is happening on the RAM memory, so a great part of the RAM would be used by the OS itself. Can I really experience performance in a LiveCD context?
I'm trying to decide between Xubuntu 14.04 LTS and Elementary OS Freya (both based on Ubuntu), to see which one would be more lightweight for my machine.
My specs are: Intel Core i3, 2GB RAM, 320 HDD
I've already have installed Xubuntu 14.04 LTS but tends to get veery slow sometimes. It could be anything (dropbox, locate database update, several chromium tabs + opening smth else, slow wakeup after suspended, etc)
The performance is a lot behind the performance of an installed system. Eg.the start of the various programs may take some time.
I would install the two systems in parallel and then decide.
Just for reference I am currently using Xubuntu 14.04 and experiencing no freezing in regards to starting applications that were pre packaged with Xubuntu. I have 4GB of RAM and about 650MB are what I regularly use with Firefox open.
What you really need to understand about Xubuntu is that not only is the Desktop Environment which is XFCE light but the applications that come with XUbuntu are exclusively selected based on how much resources they consume (abiword, firefox, parole video player). Using these apps will guarantee you a freeze-free experience, outside of that I don't know how fast or fluid your experience will be with your specs.
Regarding measuring performance in a LiveCD context, you are better off checking benchmarks of the Linux distros online as running on LiveCD will not grant you an accurate measure.
To conclude I would honestly recommend Lubuntu or Xubuntu as both are more lightweight than elementary OS.
Elementary OS recommended requirements (1GB of system memory): http://www.elementarynow.com/what-is-elementary-3/
Xubuntu recommended requirements (512MB of system memory): http://xubuntu.org/getxubuntu/requirements/
Lubuntu recommended requirements (128MB of system memory): http://en.wikipedia.org/wiki/Lubuntu
Of course when resource consumption goes down so does functionality and with that in mind I have to say that your best option is Xubuntu still but with applications that are less resource intensive.