George Groves had sparred Carl Froch before they actually fought...and we all know how that particular saga ended.
Ishe Smith... Mayweather Klitschko had enough money and pedigree, plus the trainer, and his own personalities that were okay with it, routinely sparred with some of the best up and coming fighters in addition to top solid contenders. He had already sparred a whole bunch of his opponents down the stretch of his career.