I agree as others have already stated, its definitely better to go a little larger than you currently need. You can always use the extra space as your collection may grow or could be used for other valuables that you may own.
With owning that many handguns it would be beneficial for organization and space optimization in the new safe to have a good handgun rack system. This is a few of the rack systems that my small business offers to help solve some of those issues. Many of these systems also offer accessory storage for things like magazines, speed loaders, tactical lights and such in the same space as the handguns.