Is the "Vintage Pro" significantly better than the "IV" ?
Yes. As much as I enjoy my IV, the VP (and the CP) are in another league. Different sounding, though. The VP is very like an early Thunderbird, and can do the angry piano without even trying. The IV doesn't have the top end of a VP, and the overall tone is not quite as vibrant, but it has the thunder for days. The neck on the VP is thinner (1.5" vs 1.73" at the nut). The VP is neck through, if you car about that, and the hardware is generally a bit better. The only downside I've found for the VP is the bridge adjustability is a bit too limited for proper intonation for some strings (it does get really close). The IV has the same problem, but I put a Supertone on it and it works fine.