I have a 15 month old GSP as well as the two Vizslas (and a Whippet ). I love both breeds and would have another GSP anyday. My experience is limited, however I find the GSP to be higher energy, higher strung but less needy than the Vizslas. Of course you're going to find variances in both breeds. The breeds are extremely compatible IMO. My younger Vizsla and the GSP are the best of mates and run and play for hours. When I got my first Vizsla I very nearly ended up with a GSP then. I was also looking at Weimaraners, and although I'd never have a Weim now, both Vizslas and GSPs are firm favourites.