Originally Posted by Eivind E

You can, if you're really, really super careful about tightening the plug..
I used to run them all the time because I felt like the engine ran better with them. But if you're in a hurry, or for example your pit guy discovering a dud plug just before a heat starts, you risk the dreaded gorillatighten deformation..
The taper has the same angle and everything, it's just the tapered area is smaller on the OS plug, so it's pushing on a smaller area of the head button. Hence if you slightly overtighten it, you deform the head button.

So.. if you are 100% sure you will always be super super careful with tightening it.. sure.. but if you think maybe one day you'll be in a hurry or your pit guy will replace a plug.. better run a Nova plug. Hence.. I'll just be running the Nova plugs from now on, even if they cost more and need more frequent replacement.