How heavy is he running it? We found that we were running the boat heavier than we needed to initially, and with more stern weight that we needed to. We have the LS3, and we are able to ride all day on about 5/8 of a tank with a mackin' wake. Our boat is a 2012.
A friend just bought the MXZ with the 350, and he was running about 1500 over stock with no issues. I know that if you try to run big sacks in the rear with the wedge, you will have an issue.
I agree with the on the Xstar similarity.