Is the weight of the dominix v3 comparable with the v2?
I don't own the V3 myself, but since it's a only a little bit bigger the stunt version should be comparable. However, if you're talking about a V3 with sound it's a different story - the sound will likely add enough weight to make a more noticeable difference.
Nero is right. While I don't have a Dominix V2 myself. I did get a chance to try my friend's saber. She has a Dominix V2 in Blazing Red and the V2 was lighter then the V3. Note my does have sound and AV switch in my mine.
In any case though compare to my other sabers the Dominix V3 is one of the lightest saber in my arsenal. The Lightest would be the Archon V1 (PVC)