The Corvette, and the Cadillac brand fill very different roles at GM. Corvette always has been and always will be GM's sports car. It's designed to be their ultimate expression of a high performance car that is attainable by every day people. Cadillac is supposed to be the premium brand, offering luxury, and all the goodies that come along with it. The timing of the CTS V, and the XLR relative to the vette are purely coincidence. The vette was delayed a year because Lutz decided that he wanted to make changes. That's why it won't be out at the same time as the XLR. The CTS V was a fast project, done at the behest of Lutz, so Caddy could have a sports sedan worth talking about. In the future, you will continue to see the Vette fill the role of "Sports car" while cadillac will continue to re-establish itself as "the standard of the world" by offering luxury vehicles with class, high feature content, and world class performance.
As for that fourth gen engine, you can almost bet that it'll debut in the vette. Caddy has the northstar. Corvette is the home to the small block V8. It'll end up in the trucks, and eventually in the GTO and CTS, but Corvette has always had claim to the small block, and it'll almost definitely get it first. Regarding the 7800 RPM redline, there's a lot of debate about that. I'm really curious to see if they have it spinning that high. It'd be a fun engine
Scott