I don’t think a 3U JS12ii would feel or be much faster then your current racket, just because of the possible 5g+ weight difference between the two weight categories. I mained the 3U for a while and its probably the best all-round racket, so much so that I still take it on court occasionally. I had a friend who is a Arc11 user and Yonex fan that really liked this racket as well but he couldn’t make the switch because of that Yonex loyalty.
4U would be faster, I tried it for a few sessions vs the 3U when I was deciding between the two and it was just too fast and offer no omph on power hits. Front court was a breeze tho, then again it was almost 6 to 7g lighter. Control was pretty good as well, easier and quicker to make last minute shots with the 4u.
4u BS12SE is headheavier, offers more punch and whip in the shaft and super fast, nothing cuts through the air like this frame. I would say it’s really beginner friendly. It doesn’t have much shuttle hold, frame is pretty repulsive. I found myself wanting a higher tension as well or tension just falls off faster or something.
Arc11pro 4u maybe something to consider for more control with the shuttlehold. It’s pretty fast because of the weight but not as repulsive.