mmattockx - I have a DL 50, stock muffler (LOUD, LOUDDDD) in a Goldberg Obsession. Although not a "pattern airplane", because it is both oversize limits, and over weight limits (and noise limits).... it LOOKS like a pattern airplane, sort of, and certainly flies with a lot of precision.

The resonance of the airframe where the vibes are the worst is just above idle.... at "cruise" (about 1/3rd stick with a 22 x 8), it is pretty tolerable, monitored by on-board video. Not much trembling going on during cruise.

It was very inexpensive, SIPS fuel, and will last a REALLY long time.
I have more detailed info available, PM or email if interested.

onewasp - it's pretty awesome power to weight, and the cost per flight is only a couple of cents...