Ultex sound dull to me. Not sure where you're getting the brightness comment from. I got a sample from Dunlop when the Ultex was first released, so maybe they changed the formula? Who knows.
you should all try Red Bear Picks http://www.redbeartrading.com/ those are the best picks I've tried! they have a jazz III style pick called "litte jazzer".
The picks are expensive, $20 for a pick but they don't wear off at all! you could use them forever! and if they do wear a little you can use sand paper to shave it off and fix it like brand new!
You are probably saying that it's not worth it because you lose picks all the time, but with a $20 pick I think you'll pay more attention on where you leave your pick
I just received the "big jazzer" model which is slimier to the XL Jazz III after playing the black Jazz III pick for a long time and this pick sounds so much better! the tone is wormer and the chippy sounds from the tip of the jazz III when you hit a string are gone!
Also they have an option to grip holes so that the pick doesn't slip. I have it in mine and it's great! they also have speed bevels so that you could faster things easier!