-ethi   Ethereum intensity. Default value is 8, you can decrease this value if you don't want Windows to freeze or if you have problems with stability. The most low GPU load is "-ethi 0".
   Also "-ethi" now can set intensity for every card individually, for example "-ethi 1,8,6".
   You can also specify negative values, for example, "-ethi -8192", it exactly means "global work size" parameter which is used in official miner.

I have my rigs set to -ethi 16

What does it actually do with a higher number? Without stating the obvious!

From what I can see it gives a better hashrate but thats about it.