Heh, it's not that he can't remember. It's that current Supes isn't as powerful as Silver Age Supes. That's what made Superboy-Prime such a powerful villain (in terms of power)
Yeah, I know. Now if it was Goku VS the current Superman Goku would have a much greater advantage. Although I don't follow Superman much anymore, so how much advantage is in question. After Infinite Crisis I just threw up my hands and gave up on him.
Although Silver Age Sueprman never used his powers really right. He could fly throught he time barrier, but his villains include .... the Prankster. Yeah. I'm not sure how many of his problems couldn't have been solved by going THAT FAST and just smashing whatever villain was in his way. Hell, even the magical ones, like Satanus, wouldn't even be able to see him coming, much less react in time.
Edit: Goku can't break his time barrier but Superman's speed can. Case closed to me. It's just like Superman or Batman not beign able to channel their Ki. Just as Superman just can't channel his Ki, Goku just can't go as fast as he can. Goku's dimension switching abilities are unrelated to his speed.