Hate to break it to you but if I were you, I would go YS. I just shelled a brand new OS C spec. Its the 4th OS in a row that has failed out of the box. I won't buy another one. I just finished installing my new YS in my heli. Its nice. I hope it runs as well as people say. Look at all the writeups in the engine forum on OS. They have really cheapened up the line. You can buy one, but why risk it when there are better engines on the market. YS is the same price.

The piston on my C Spec came apart in very few runs. That was the last straw. Good luck on whichever you choose.