Kinda off topic..... but, I've had 3-1/2 Vipers, each one felt different and unique from the other. I think the one I've got now is pretty good, but I think the one I had before was the best I've had. I also had one that I sailed for half a season I just did not like. But, I know the Viper pretty darn well, and if you're just test sailing something those small variances probably aren't noticeable unless you've got a ton of time on that model already.

I don't really see the point in a test sail. I've never done it. Assembling the boat with the current owner if you are unfamiliar with it is a good idea so you know the little nuances, and so you know all the bits and pieces are there.