The biggest negative to the inside extension is the handling issues raised by AeroplaneDriver.
Moving the line of thrust (where the engines are doesn't matter that much) further out from the centre-line reduces the general handling of the aircraft & is a major concern if you lose an engine, creating extra yaw, especially, both of which would require larger vertical stabilisers & control surfaces, which would increase drag & slow the aircraft down.
Increasing engine power will give you more speed, to make up for the extra drag, but it won't help with the handling issues & may require even larger vertical stab's & control surfaces for engine-out handling.
My vote is for outboard of the prop's.