The fact of the matter is you're set on the idea of the Reliant being bad-assier than the Enterprise and nothing is going to convince you otherwise, so there's no point in further discussion on this point.
Naah. I'm just pointing out the glaring weaknesses in your arguments about how some other explanation must be the more likely one. It's extremely difficult to see how Spock could assess the ongoing situation objectively and realistically, but we should expect this one character to be objective and realistic. So the mechanism by which Spock convinces himself of the things he then reports to Kirk is interesting to the extreme. And if the writing of the movie doesn't offer Spock enough data, then the data must come from things not written in. One possible explanation is that Spock read the specs of the opposing ship from a database; the other is that he read them from his sensors.
Personally, I hate the idea that the rollbar phasers, physically the smallest aboard the two ships (save for Kirk's shuttlebay phasers), would somehow have more firepower than the triplets of double banks on the saucer surfaces. Khan's superiority hopefully stems from some other fact. But that's just a side issue in the hunt for the means by which Spock is aware of the (current or inherent) difference.
Khan did not have a clue were Enterprise was
Sure he did. The
Enterprise had just moments ago delivered Kirk to Regula, so she
must be nearby, and there aren't all that many places for her to hide. Khan listens in on transmissions from her, which should already give him an easy fix. But nothing suggests Khan wouldn't have had the exact same sort of tactical display available.
...He's just pleasantly surprised later on that Kirk's ship actually has set sail ("Thar' she blows!") and has become worthy prey, just in time for the big battle now that Khan's own repairs are completed. He couldn't have come hunting for Kirk earlier on, as Joachim was still toiling with the machinery, regardless of whether he knew where Kirk was or not. I'd surmise he only snuck next to Regula I after seeing that Kirk's ship was
not there, considering his own ship's state of disrepair...
That tactical display tells little or nothing about the opposing ship as such. We get one parameter: "Orb Z". And that's pretty much it. Whatever sensor data Spock is getting must be coming through his other instruments, which we don't get to see.
Timo Saloniemi