I keep getting this image in my head of a jedi knight trying to take on a space marine Librarian... A few blows are exchanged.... Jedi speed being equaled by veil of time... until the Librarian get really angry and pops the Jedi's head with either the warp... or one of his bare hands...
But seriously... I'm not sure about the size of the empire vs size of the Imperium as I am no Star Wars buff, but when you watch the movie... doesn't a Space Marine Battle Barge look a hell of alot more intimidating than a Star Destroyer? And, those piddly little lasers on the faces of those ATAT Imperial war walkers seem pretty pathetic compared to the volcano cannon for example strapped to the arm of A raging metal war God (Titan anyone?). Not to mention the Imperium is constantly wracked by wars, its citizen base are crazy bastards to start out with, the imperial guard toughened by milenia of tireless combat, they already seem a match for crack Empire Storm Troopers, without brining in the space marines... and the sisters of battle... and what happens when the assassinorum is unleashed on the Empire?... how long would their leaders remain alive with Vindicares stealthily preparing to deal out an inglorious death from a balcony a kilometer away? Or callidus assassins within their midst? not to mention culexus... *shudder*. I can imagine the look on a jedi's face just before getting shot to pieces when he realizes that his force isn't working due to the eversor/random non-assassin trained untouchable a few meters away. And the inquisition..... I'm pretty sure they would make Palpatine sweat. And what of the death star? the destroyer of worlds? Well... Isn't exterminatus pretty 'normal' in the Imperium when a planet is beyond redemption? It doesn't blow up the world usually, no. But when the entire world is burnt to a crisp by firestorms and obliterated of all life by a hundred viral agents... I just get this image of a generally peaceful empire being speared right through by a diamond hard war weathered civilization that knows no peace... Hell, imagine the reaction of the Star Wars Empire when they meet the other kids on the block other than the Imperium... Want to see A storm trooper sh** itself? Show it a giant crimson armored Khorn Berzerker, chainaxe screaming, baying for blood and skulls... Bloodletters popping into existence... Or even the Dark eldar... their depraved minds dedicated to misery and torture... I think they would be packing up and moving a couple galaxies over after one peak at the orks.... And the Imperium is fighting against all of these every day, dieing, screaming, bleeding, struggling, and holding them back, a daily life struggle for an entire civilization... No... I do not believe it would be a war... The first few battles would be brutal... but from then on... it would be a rampaging slaughter... Broken men screaming and sh**ting themselves as they are lifted high, impaled on the ends of rending Eviscerators, high over the head of zealous, faith crazed Repentia, bathing in the blood and entrails raining upon their upturned rapturous faces. Men crying as they rock back and forth, clutching themselves as they weather precise and merciless Imperial artillery bombardments, only to meet their end on the bayonets of grim faced guardsmen who has seen the face of hell and lived to continue onwards, knowing they are just a fragment of trillions of others... hardened by the horrors of a universe of bloodshed. And annihilated by the armored angels of death who walk through the hail of laser fire like gods through rain, their mighty bolters singing praises to the emperor with every ear piercing shot, each mass-reactive round penetrating thin white armor like paper, detonating within fragile flesh to turn men into twitching piles of bloody flesh, only to be trod upon by the great soles of the pinnacles of mankind, running before the disciplined fire and the oh so implacable and expressionless helmets that bay forth challenge and praise to the Emperor. Before the relentless Imperial fleets... The numberless Guardsmen... The fear invoking and immense tanks... The zealous and fanatical Adeptus Sororitas... And the Fearless, superhuman elite Adeptus Astartes... They would fall...