The Nexus 5 is the same size as the 4.7" iPhone 6. I sold my Nexus 5 for an HTC M8, which I thought was too big at first and considered down-sizing to a 4.7" iPhone 6. But the 6 would be a downgrade in terms of resolution and battery life, so now I'm thinking of getting the 5.5". The 5" M8 actually isn't too bad, so maybe I could et used to the 5.5" 6+.I thought the same when I sold my iPhone 5 and bought a Nexus 5 (I know it's only 5"). I thought I would use my iPad Mini less, but no.
I'm selling my Nexus to buy the new iPhone - having now tried Android, I'm not a fan. However, because I'm used to having a larger phone, I think I'll go for the 5.5 iPhone, and I can't see it replacing my iPad.