I posted this to the WB-Sim Discord. This is no official answer, but the WBSim seems to use the value of 1.0 (have not verified yet). The Value of 4.3 for the G1000 therefore seems to be way too high.
Guy is saying it can drop between 3000-5000fpm in a slip, which for sure doesnt seem right.
Again, i have not doublechecked this, just parroting at this point.
The mistake seems to be the value of 4.3.