For those looking to do the same thing, I ended up going a different route: I used the same technique used in the  ParticleSystem sketch in examples/Particles to create a texture that holds the desired size for each individual particle. I also ended up using a texture to store each particle's individual color. Also, since the size and color values were already computed in the sketch, I skipped the "MovePart.xml" texture filter step and wrote directly to the data textures using the GLTexture.putBuffer() method.
My sketch which was running at 6 frames per seconds in OPENGL is now effortlessly achieving 30 fps.