(Outdated- This is with full render distance of the splashes, my new set of splashes get rendered at a smaller distance thus saving frames)
If you have seen my rain videos you would know about how badly the splash particles effect frames. Well, I calculated a set of % for you with their % of frames lost. Please note the density is 100%*. Now, this isn't perfect and it is tested on my system**.
// Low % = 15; FPS Loss = 28%
// Good % = 35; FPS Loss = 46%
// High % = 50; FPS Loss = 58%
// Extreme % = 99; FPS Loss= 75%
As you can see extreme is, well, extreme. With a 75% loss of frames. This is only recommended for very extreme systems. High is a little better but over half of your frames lost isn't good.
* I pretty much modded the density code to its extent with out the engine dieing on me. So smaller density %'s go a long long way.
** These % are not calculated with NPC's and every other frame killer in mind.