By Wookie, the maximum acceleration is ">2,300 g"- greater than 2300, but with no note or citation to back it up.
Dr. Saxton- specifically in http://theforce.net/swtc/propulsion.html
uses photoanalysis and geometry to extrapolate their acceleration from their speed across the background at Endor, and twenty-three hundred 'g' is the firm lower limit that evidence will support, depening on the assumptions made about Endor in particular.
We know from the main site- look for the part on why size matters- that the Executor class have to be orders of magnitude more heavily built than the Imperator to survive the same acceleration, and that speed was the speed of the fleet, the speed of the flagship to be precise.
The Executor class's power to weight, judging by their observed armament, is also lower- so no, there's no absolute proof that the Imperator/Imperial class's thrust is higher than 2,300 'g', but there are solid reasons for it to be more than that, and solid potential for it to be more than that, and comparisons indicating it ought to be more than that.
For added entertainment, look at the section on manoeuvrability, especially the bit about the actual physical potential of off- axis main engine thrust.
You're conflating sublight and hyperdrive performance. 'Point X' has nothing at all to do with ion drive, it's an index number, a relationship to a benchmark established as standard (and canonised in the ICS, incidentally) for hyperdrive performance, and that performance is expressed in time.
A Standard One hyperdrive takes the benchmark time over a given course, a Standard Point Five takes half the time- which I reckon is what Han meant by "she'll do point five past lightspeed", although there really should be a comma in there, it's not sufficiently clear that the meaning is that once on the other side of the light barrier, her rating is point five. Standard two is twice as long...et cetera.
Yes, this argument has occurred many times before, in case you were wondering.
To go back to answer an earlier point about the Executor's shielding, I think there are filmic reasons why she's not going to be shielded in proportion to her mass. Practical reasons, more later after a little thinking time- let me get back to you on that one.
The filmic reason, of course, is that it's impossible for heroes to slay properly behemothesque ravening monsters unless the ravening monsters have a suitable weak point. Although I have to laugh at the idea of how Piett would react to having that description applied to him face to face...he really didn't suit it, did he? A competent technocrat, but not a natural warrior spirit- perhaps Executor's real weak point was her command staff. Piett wasn't monstrous enough.
Ackbar didn't order component shots, but I'll grant that perhaps he didn't need to. If that was the only way to do it, and his captains knew their jobs, they would have come to that conclusion themselves without being micromanaged to it.
So, point in favour of it being the specific centre superstructure/bridge shield panel that was pounded down...hold it a second. How close is Executor's bridge to the geometric centre of the ship- to the prime aiming point? Hmmm.
Anyway, there are too many EU instances of ships of the class being destroyed far too cheaply than should have been the case for me to be comfortable with, and while some of them were cheap shots and writing without a sense of proportion and scale to hand, the established pattern is not good.
The other reason to suspect something funny in general is up is the respective shielding and armament of smaller ships, and how they seem to change. Small ships carry shielding in proportion to their weapons, not their drives and total power rating- they're drastically underprotected, evidenced by the fact they're able to hurt each other at all.
I actually suspect a bell curve, although I'd hate to have to swear to that based on the data to hand.