Energy Cell is optimized for spin performance and creates a slightly different feeling than the regular Rasanter sponge, although this would only be noticeable when comparing R47 and R48 with the same nominal sponge hardness of 47,5 degrees. Catapult for me is a side effect, and speed - well, I couldn´t really tell if a topspin flies faster with R48 than R47...
What´s really interesting is what I wrote above about the varying degrees of the "plays softer" effect. This is very probably caused by the different cell-wall thicknesses. R53 will be surprisingly soft for such a hard sponge, but of course not a soft rubber as such. I can only compare it to GEWO Super Select 53, which is way harder overall. Evolution MX-D also feels a little softer than you´d expect, but it is not the direct equivalent, those new ESN rubbers are different.
R48 also feels a little softer than R47, but with all the different topsheets of the current rubbers you will doubtlessly find other 47,5 degree rubbers that feel softer. Again, Evolution gives a good example with EL-D, but that feels a lot softer than R48.
R45 is just an amazing rubber on its own. The first sheets I had almost rivalled R48 in speed and spin performance. That is why if someone is looking for a nicely controllable 45 degree rubber I´d recommend trying Hexer Grip. R45 is a power package that happens to be a little on the softer side. Again, and still not meant for a direct comparison, only in overall feeling and softness, the new FX-D is much softer.
And if you ask, I´d take any Energy Cell Rasanter over any Evolution "D" of corresponding sponge hardness, but that is a personal thing.
The other rubber I have found to play softer than it is rated, much like R53, is K3 which I have settled on and slightly prefer to R53.