After several more test flights and some contemplation, I reluctantly decided to go back to the stock motors on the 350 QX.
The Multistar motors are of high quality, smooth and powerful. However, with every power increase comes an increase in battery demand and the extra load on the ESC's expressed as heat and the commensurate battery impact concerned me in this instance.
I encourage you to follow your mind and to go for what you want to try. I doubt there is any danger in using the Multistars, I'm just very cautions. By all means have fun and keep em' flying!
God Bless!