I can't see how the cautious Roy Jones Jr. has a chance in this fight... Byrd would flick out his jab all night, and Jones wouldn't respond at all. Byrd was taking alot of shots from Wladimir so I don't think Jones has the power anymore to knock him out without giving him a complete night of beatings. Anyways Byrd is similar to an extent to Tarver, but more technically sound, and has quicker hands, and he would be dropping that added muscle giving him even more speed. I think even Prime Jones would need awhile to figure out Byrd ... if Byrd fought more like old Byrd, but I think in the end Byrd couldn't defend against Ike's right hand, and he couldn't defend against Wlad's right hand so my verdict is...

Prime vs. Prime at cruiserweight: Jones would make Byrd eat as many right hands as Jones wants.
Now: Jones would be hesistant, and this would look worse than Tarver vs. Jones 3 because Byrd is also cautious, but in the end Byrd would win.