Yes I did. Also I did use GPU-Z and everything looks fine. Everything says its fin but I notice no difference.
Just run a benchmark. 3dmark is a free download and will tell you exactly whether or not XFire is working through your score. Run it with XFire OFF and then run it with XFire ON. Compare scores, easy.
Regarding v-sync - yeah it will set an upper frame limit of 60 (on a 60hz monitor). If you are playing games where the minimum FPS isn't dipping below 60 then turn up the settings - you can turn off v-sync for evaluation purposes but having it on is usually best.