HOLY CRAP! 12.5 pounds?? Wow. Man, my 7.5 pound J5 (another brand) would probably feel like it was floating out of your hands!
Seriously tho, I generally like the lighter basses for my lower back on the usual 4 set gig, but there's something about that 9-10 pound range for a 70's style bass that really works well. Most of my stuff is just under 8 up to 9 pounds, with the exception of my SB and my Geddy (also a 70's style of course). That bass is pretty much right at 10 pounds tho, and that's definitely my hard ceiling. If I play that bass all night (haven't in a long while), I can feel it at the end of the night... and I refuse to stand still or especially sit on a stool. I gotta' move, so even a one pound diff in a bass is really noticeable to me.