I would go to 15% nitro, I have ran 10% on them for years and thought the performance was good until I went to 15% synthetic, its much smoother. (I run only saitos so I dont know if it applys to brand X). And yes running too rich you can also go through plugs quickly. During break in when running the motor super rich I might go through 2 plugs before I get into the air. Then another one after about 4 or 5 flights until I begin leaning it out some. Dont ask for the scientific info on this, I just know it happens. And beleive me I have burned a lot of Nitro