Kyotaro. K-1 HW Champion. Overeem was one of the decent k-1 HW's. Boxing match with Kyotaro. [yt]8zT2J3iXJJ8[/yt]
Kyotaro got taken to school by Schilt, and even Mousasi(an MMA fighter under K-1 rules) even an old war-torn Jerome Le Banner gave him all he could handle, actually JLB could have won, but he refused to fight in the extra round that would have determined the winner. Kyotaro isn't even close to the best K-1 has to offer, you don't know what you're talking about.
Matt Skelton, and Ustinov are former K-1 kickboxers who made successful transitions to boxing(they weren't even elite k-1 fighters). To say there aren't guys in K-1 who could transition to boxing and do reasonably well is just plain false. I think with the right preparations, the likes of Ghita, Saki, and Spong would do reasonably well.
Hari has one of the worst chins in K-1, Overeem was also juiced to the gills when that fight happened, and Badr kicked his ass in the rematch.