Actually, a 2x4 grid C&C cage (grid cage) has just a fraction more floor space than a 2x5 ft conventional cage (the 2x4 grid C&C is 70x140cm, therefore fractionally bigger to 60x150cm).
So if you are pinched for space, I would recommend going for a 2x4 grid C&C cage with a hayloft or a second story to provide plenty of extra space while still fulfilling the minimum requirements on ground space to satisfy any rescue.