I could be wrong, but I have a worry that since you may end up going to a higher or lower barometric pressure F8tlSHO, the MBC could become a bit of a pain, if your desired boost levels change. I guess you would know the scaler, but definitely something I would want to monitor on the X4, OR if you are feeling fancy add a cheap manual boost/vacuum gauge into the line, maybe even add two reference locations (one pre, and one post, MBC, so you can see the effects it has).
I am not a MBC guru, but would it do anything to the reference when pulling vacuum, could be a simpler way to see how much you are changing things.