Certainly the Borg would decimate the Empire.
If Batmobile Voyager can beat the Borg, then I doubt the Empire would have much trouble.
Since nobody appears to have clicked my links, then I may as well repost some of the information. Yeah, there's an anti-Star Trek bias on the part of the guy writing it, but if a guy's right, then he's right, irregardless of what his attitude is. From one of the above links (Images don't appear, so you'll have to click the links for the graphs)...
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The Lazy Man's Method
Simply grab figures from the official publications. Of all the voluminous Star Wars and Star Trek publications out there, only one for each series gives meaningful specifications in real-world units: Star Wars Episode II Incredible Cross-Sections (SW2ICS) and the Star Trek Next Generation Technical Manual (TNG TM).
http://home.comcast.net/~renef78/Vs01.jpg
As you can see, the officially published figures are massively in favour of the Empire, even if you disregard the fact that an Acclamator is not a particularly powerful warship by Imperial standards (an Imperial Star Destroyer is roughly 10 times larger (by volume) than an Acclamator and presumably 10 times more powerful, even if we disregard the fact that an Acclamator is just a transport). In fact, the only way to generate a remotely close match between an Imperial ship and a Federation ship is to use a small patrol craft such as Jango Fett's Slave-1:
http://home.comcast.net/~renef78/Vs02.jpg
Even this seemingly Trek-biased matchup seems to heavily favour the Empire, with Jango Fett's small patrol craft able to hit the Enterprise-D with much heavier firepower than it can dish out in return. Small wonder, then, that despite the simplicity and convenience of the lazy man's method, most Trekkies prefer to avoid it.
Just What You See, Pal
Some people prefer to pretend the books don't exist on either side, and talk about only the movies (or movies and TV shows, in the case of Trek). This approach has strengths and weaknesses; the visual look of each series is often more consistent than published material (particularly in the case of Star Trek, where the TM contradicts itself repeatedly and has several astonishingly bad science errors. Moreover, the ST books' status has been officially stated as mere "speculation" (see John Ordover), although SW books are supposedly "quasi-canon" (see the Star Wars Encyclopedia foreword). In any case, a lot of people prefer to stick to the shows and movies regardless of what the "official" stance is.
Having said that, the comparison is little better. In Star Trek, most of the figures from the show are reasonably compatible with those from the TM's (not surprising, since the people who worked on the TM also worked on the show), and in Star Wars, most of the figures from the SW2ICS are based on observations of the original trilogy (from Dr. Curtis Saxton). There are limits to how inaccurate one can reasonable expect the TM and SW2ICS to be, and sure enough, analysis of direct observations from the shows and movies tends to generate similar results, albeit with more ambiguities.
Note that it is difficult to gauge the effect of weapons in any meaningful sense unless they are applied to inert objects (if a shell hits an aircraft wing-tank and causes the plane to burst into flames, you cannot attribute all the energy of the resulting conflagration to the shell). This means we need to look for weapons striking inert objects such as rocks, planets, asteroids, etc. I'm afraid this is a rather complicated subject, and you should really look at the rest of the site if you want to know more. However, the following table should help clarify matters:
http://home.comcast.net/~renef78/Vs03.jpg
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Getting down to brass tacks, if the Enterpise D can't even match up with the Slave-1, then what hope would it have against a Star Destroyer?
Yeah, the original poster said "throw everything in", but that's the only way Star Trek wins. If the Q show up and use their omnipotent powers to wipe out the Empire. Otherwise the Federation, Klingons, etc are toast. Not only can the Empire run rings around them with their hyperdrive, but their weapons are insanely powerful in comparison. Slave-1 can tear through the Enterprise, so one can only imagine what a Star Destroyer would do to a fleet of Federation ships, or a Borg cube. And that's one Star Destroyer. Throw a fleet of Star Destroyers into the Star Trek universe, and most everything in the Milky Way would be reduced to ashes.
