Just to try and help clear some things up (been a SW Fanboy WAY too long
)
#1: The equatorial is exactly that... the trench around the equator, all it has is docking bays and more guns and more docking bays..
The actual "Trench Run" is at the very north pole of the death star as in the briefing it says its a small thermal exhaust port they have to shoot torpedoes in... and you wouldn't really want a exhaust port for something like that amongst docking bays
#2: Regarding the X-Wings speed, when Luke flew into the trench he got R2 to increase the power to the engines only, this would have lessened some of the power from other systems to gain this little bit of extra speed (lasers, shields etc).
Closing/opening their S-Foils is for;
:Easier Storage
:Gives the lasers more accuracy and range (width/height not distance)
:Allows the craft to actually be flyable in a combat situation in a atmosphere
#3: The DSI and DSII are 95% the same except for the fact that the DSII was less powerful in the fact it was mainly going to be used on starships/planetary bases rather than outright destroying planets and it also didn't have a open exhaust port like DSI which is why the rebels had to strike when it was uncompleted due to the fact that they could access the power core.. If the DSII was fully completed they rebels would have been majorly screwed
Edited. Smiley code fixed - TopAce