Would a 7mm sliding genioplasty to compensate for class II malocclusion look unnatural? (Photos)

The only way to have better insight into the amount of movement that looks natural vs unnatural to you is computer imaging. See what the difference is between 5 and 7mms...which will be very hard to see as neither one will likely look unnatural which for a male usually may occur when the chin projection goes beyond in profile a vertical line dropped down from your lower lip. For that to occur in your case the movement would have to be closer to 10mm+.

Your lower jaw is underdeveloped genetically and the 'throat/chin' distance is quite short with an obtuse angle....so you do need a notable advancement to achieve your goal. Don't focus on the 'number' but the overall appearance and balance you want to achieve. The profile result determines 'how far' to move the chin; since all soft tissue densities/thickness affects how it looks after the procedure.