The maximum (and unchangeable) particle limit is 4000, after which fireworks quality begins to degrade through fast expiration.

How low is this limit? A single firework containing 3 firework stars with trail effects is enough to *hover* at the limit.

In short: A single firework containing more than 3 trail effects, or more than 3 trail effects launched at a time begins wasting diamonds.

Allowing more particle control would be a nice feature.

Here's a mod demonstration which concludes with a very laggy 32k particle limit: http://www.youtube.com/watch?v=lGbA8kTGSZQ