Yeah lol. The J stepping chip seems very new so it also pretty rare and not all J chips seem to hit the speed you've got. People shouldn't expect too much from the X5960 as the vast majority aren't great for overclocking.
Its not actually new. It has been there since the 12nd week of 2015 iirc. The chance of you getting a J batch brand new from OCUK is actually much bigger than an L batch. I had been binning 8 pieces from Costa Rica, Malay L and Malay J, 6 of them passed 1hr asus real bench stress test at 4.5Ghz with less than 1.3v. The Costa Rica batch was manufactured in 2014 didn't make to 4.5ghz