I have the dual set up on my 216. I'm not sure it makes much difference. You have to consider that your throttle is opening twice as fast, so it feels like a big difference. I've noticed that I do get a smoother idle, and a little improved mileage. You can run more timing advance too. It also looks really cool!. I've had my set up on for about 12,000 miles now.
I seem to recall that you can run a 216 up to about 6000 rpm, I think I read that in the California Bill book, but that's with all kinds of stuff on the engine, like double valve springs, and magneto ignition, with dual points, etc.
I think the splash oil gets a bad rap these days, and its undeserved. They were used for millions of miles in trucks and cars, and we have much better oil these days.
That's my opinion, I'm sure others will disagree, and that's okay too!
