Smoke particles on smartphones - which size is better?

I would appreciate if somebody could answer the following question. What sizes are most suitable for textures that are used as particle sprites? Particularly particles that are imitating smoke - which sizes up several times over its lifetime. Is it better to have them small (64x64 - texture will have to get stretch) or large (512x512). Of course the main reason I’m asking is as always in those cases - performance. Thanks in advance for the answer

I’ve found this information useful regarding the texture sizes, to keep in mind as a general rule:

“Keep the size of textures as small as possible while still looking nice. If your graphics card does not have enough memory to keep all the textures in memory at once, they will get placed into regular system memory and uploaded to the card during rendering”

from: http://wiki.unity3d.com/index.php?title=General_Performance_Tips