Never really tried these before, same goes for boids.
Here’s a simple animation I rendered from my test.
There’s 1080p available, Youtube quality makes small moving particles into a mess tho 
Neat, I have not done any work with keyed particles either. Care to share a BLEND file with the setup?
Thx 
Here is the scene like it was for the rendering, except particle count for all systems was reduced from 10 000 to 100. Reducing the number of particles made .Blend file size drop from 100MB to 1MB 
http://www.filedropper.com/keyedparticlestestt
I’m not sure what’s a good site for blend sharing…
Cool. I switched from cubes to planes as objects for my tests. When the particles are small like this is reduces vertex count by half.
Hehe, if you want to minimize the vertex count for 3d particles, tetrahedrons are probably the best objects for this. 
They have 4 vertices and 4 triangles…
If you want to increase rendering times in BI, reduce the size of the particles. BI starts to struggle when it needs to calculate a correct color for a pixel where there’s large number of small objects overlapping.
Tutorial here.