Superman: Can he maintain enough focus to control the 'mph' of his ejaculation?

Why would I ask that? Well, this is just as good as the questions regarding the Smurfs: are they mammals, do they lay eggs, or do they reproduce a-sexually? That's a good fucking question. ...no pun intended. Pointless, but fun to think about.

So, when Superman is beating the knuckle children, or doing the nasty with Lois, is it lethal?

Superman can control his speed, his strength, his breath, his heat vision, etc. But the sheer act of sex can make one distracted and 'lost in the moment', and if he's as anatomically correct as he looks in that suit, then one might logically assume that to harden his shaft blood must fill the spongy tissue of his penis. Hence, there could be a potential lack in coherency during the act of sex.

As they copulate, Superman is overcome with sensation, his focus begins to wane as intensity increases. Is it plausible to assume that if he's not controlling his every function to the fullest, his sperm could shoot through Lois (like a speeding bullet) through her head, through the ceiling, out of the building, into the sky, and punch a hole in a passing 747 strong enough to cause serious pressure complications?

Well I certainly think so.

In one universe, there's evident proof of this being an acceptable theory: There was a parody comic (The Pro) in which Superman got a blowjob from a prostitute (you should read it). This resulted in him having her move out of the way and he hit a 747 and made it crash.

Alternately, in the actual comics, he's had sex multiple times and nothing's happened, which supposes that he does have the ability to control himself. Or maybe it's just with Lois that this is possible. I leave it in your hands to speculate!