Don't get confused between WOT static rpm on the ground, and WOT in level flight.
Setting for 5100-5200 RPM, WOT in level flight will have you way over pitched in my opinion. Setting for 5100-5200 WOT on the ground will have you way under pitched.
Most RV-12 owners have found that setting up for about 4950 WOT static on the ground, gives good overall performance.
This will give you very good take-off performance and good cruise performance through a wide range of altitudes.
The wide range cruise performance comes because you will have a prop pitch that will require you to throttle back some in level flight at lower altitudes, but, you have more throttle to use as you climb, thus maintaining good cruise #'s.
Now if you want an airplane that operates more like the Piper or Cessna you have always flown, where the only way to over speed the engine was to point the nose straight down, then use a lower static RPM.
It will give you real good cruise #'s at lower altitudes (you will likely exceed the 120 Kt LSA speed limit).
The down side is that you will have poorer climb performance, poorer cruise performance if you ever cruise up high, the oil temps will tend to be higher, and you will be lugging the engine more in climb (Rotax specifies a minimum of 5200 RPM during high power operation (full throttle / high manifold pressure). That really isn't possible with most LSA because of the compromise induced by a fixed pitch prop, but using a static RPM of about 4950 gets us very close (climb RPM of 5100-5150).
Keep in mind that while the engine is breaking in, all of the RPMs will climb a bit (particularly the idle speed), so setting for a slightly lower RPM (50 or so) is not a bad idea.
Also keep in mind we are talking about very small pitch changes on the prop.
The difference between over pitched and under pitched is less than 2.0 degrees. When fine tuning, I am making changes of only about .2 degrees.