Have you already listened to songs made with VOCALOID 4? I think there's a lot of improvement from V3 to V4. For example, this VY1V4 MIZKI cover of World Is Mine... It's so realistic <3 youtu.be/IIK55iBClSQ
Oh, and I'm waiting for Luka V4 and V4X' songs ╰₍༼◠∇◠༽₎╯