Why wouldn't you think the 2.53 would have a c1 stepping??? Imean there is supposed to be a c1 stepping for 1.8,2.0,2.26,& 2.4ghz as well so I would surely expect a 2.53 c1.....plus intel has it listed at its spec code page....
supposedly that is a definite clue...the 1.525v that is as the 2.8ghz chip was the first c1 stepping chip to be released and it was the first migration to the raised default vcore....