Particles are visual effects. They shouldn't drain your CPU resources. Unity's built-in particle system runs on the CPU and thus is very limited in terms of particle count. GPUs however are built for parallelization and can compute and visualize extremely large amounts of data. That's why I programmed a GPU Particle System for Unity.It's able to handle millions of particles per system and allows amazing visual effects. It also comes with a fancy custom editor to quickly change it's many parameters.

Check it out on GitHub