Here is the deal, The size by velocity is mising from the editor making us unable to control it’s size over an amount of velocity which causes us to find other work arounds to solve / fake it.
Now is it natural that it’s missing was it replaced by some other “function” in cascade?
By changing the TypeData to AnimTrail I managed to unlocked the Size by Speed, not sure if this helps but maybe you’ll find what youre looking for in a different type. Lets just hope it gives you the desired end result 
Would have to re-set the system to match the needed settings of AnimTrail. However will give it a go see what happens.
Thanks for your reply Daniel.
GPU Sprites has Size by Speed function as well.
There is no point to load particles in GPU if they are already cheap.
However thanks for the reply.
I’m not sure but I don’t think they are more expensive. They don’t support some functions however, like sub image index and light.
That’s what i said. They are not expensive, GPU particles are loaded in GPU to remove stress from your CPU. If the particles i already have are not much of memory / process consuming then there is no point for me to load them on GPU. If they were heavier then there would be a reason to make the GPU sprites.
Hi Chris,
As others have mentioned, Size By Speed is an available option for Emitters with the DataTypes of AnimTrail, GPU Sprites, and also Mesh Data. I am not aware of the reasons for the limitations of this module to certain DataTypes, but I have made a request for it to be expanded to be included across all types. I will let you know if it comes back as not an option.
Cheers!
Thanks for the reply.
Hi Stephen, this option (alongside Size Scale by Time) was always available for CPU Sprite Emitters in UE3. It would be great to see both modules return!