Oh geez, you're going to get confused on this one!! Still.... this is my basic use, either a Xenar or a Xenotar.
I would say that yes, there is a difference in rendering. The Xenar is 'smoother,' the Xenotar is 'crisper.' I see it in what might be called local contrast? The Xenotar can have a snap and crispness in how it renders an object. The Xenar won't have the same local snap. If I had a couple of prints in fornt of me I could point out the differences, but on the internet they will be lost.
So, that last comment should be noted- on the internet you'd be hard pressed to tell them apart. By the time you account for light, processing, etc., both lenses will be good and will stand up next to the other, in prints or on the internet.
What is making you think about a new camera?