I think I've answered this one at least three times heh
Ultra - very heavy and a little mid scooped. Probably the ultimate metal module, unless you consider:
UltraXL - like the Ultra but with a little more high end for cut. It may appear to have more gain because of the way the ear works but I think it's same as the Ultra and they can be dialed very similar
Ultra Lead - this is a mid heavy, singing lead type module...think Santana. Not super high gain and not really suitable for anything but leads to me.
Yeah, I asked the same question as a newbie back in Aug, and JKD answered it then too...and he's right on target. The Ultra Lead wasn't my thing but the XL is a great lead module; pretty close to a 5150 lead channel.