It would be minor. The short answer is that it would be possible to have any of these systems that don't provide for overhangs and you'd be able to do the analysis, which can give you insight as to what impact it would have upon proportionality.
Remember that MMP is a moderate form of proportionality. It's not an absolutely pure system. There will be levels of disproportionality, and the question will always be how acceptable that is and where it would fit in the balance between proportionality and the desire for stable, effective parliaments and stable governments.