I really like the Gibson Thunderbird Studio bass. It was my first T-bird, I got one in cherry, a 4 string, and I still have it. I liked it so much I also got one in ebony! First one I paid $1000 for, the second $900.
I think they are great basses, and am not sure why they were discontinued. Solid, cool looking, and sound very similar to the IV bass, though a little darker to my ears. My ebony bass has a chunkier neck than the cherry, which is a little fatter than the IV version.
I believe the Studio version has the same PUs as the IV, and the bridge on the Studio is superior to the tri-pod thing on the IV, IMO.