old subject..... I have been racing for 7 seasons with o-ring and can testify that non of my race finishes would have changed by having a non OR chain.
although when flexing by hand a (cold) o-ring chain seems like having more friction, in a race the chain heats up big time, the resistance drops noticably. never mind the fact that a non OR will fling its grease out of the bushing areas in no time and there's no way to push back in there the lubricant. so after maybe one race the friction is bound to be WORSE than an OR....
simon 42, a member here with a long history of racing and tuning has witnessed dyno sessions to check just that and the difference was negligible after the OR chain heated up.
I like to rivet mine, but heard also about cleaning the side plate with thinners, and putting a nice blob of RTV on the clip.