There were only XLRs in 2004 & 2005.
Starting in 2006, there was the XLR and the XLR-V, which was supercharged. It was at that point that people started referring to the XLR as the "base" model.
The XLR has adaptive cruise control and the XLR-V does not.
The XLR-V is supercharged.
The XLR has 320 hp and the XLR-V has 443 hp.