As does SW, they are almost identical in speed, but the empire has a range advantage due fighting at the same ranges, but having guided missiles.
There's several problems with this statement.
1. The acceleration figure I gave was derived for a vessel the size of a small moon. Further, calcs derived from the 40K novel Sabbat Martyr gives an Imperial capital ship an acceleration on the order of 8000-9000g. An ISD-II can manage 2300g.
2. Does the Empire really have a range advantage? Because 40K ships fight at 100s of thousands to millions of kilometers of range, and SW forces tend to fight at closer than maximum range due to EWAR.
3. Many, no, almost all 40K forces have ship-to-ship self-propelled, guided ordnance. Said ordnance has tremendous range. In fact, the only force that is known not to employ any ordnance weaponry (torpedoes, fighters/bombers/assault boats), are the Necrons, but the Necrons really don't need it.
4. SW ships rarely use guided missile weaponry for capital ship combat. I'm not saying that they flat-out don't, just that's it's sufficiently rare that saying "Empire uses guided missiles=advantage" is rather vapid and dishonest.
But on the other hand, they are psychic enhanced. Not the most reliable.
A psychic-enhanced sensor system doesn't automatically mean that it's less reliable than a non-enhanced device. I'll also note that not every sensor system is tied into an astropath. Most are tied into a cogitator, logic engine, or servitor.
Incidentally, psychic-enhanced sensory apparatus do confer a significant advantage in countering any stealth techniques employed by the Empire/SW forces, as you can't really hide the person inside it, and it's unlikely to use a droid pilot due to anti-droid bias in the Civil War&beyond eras.
Yeah, but the Empire is much bigger, and reliability and resupply aren't the biggest issues when it only takes a few hours to get more equipment.
1. The Empire isn't "much" bigger. As per one of the novels, I can't remember off-hand, the Empire consists of 1.5 million full-member planets, and 69 million colonies. The Empire isn't even "bigger". It's, at the least, of parity in size to the Imperium, but some estimates place the Imperium as having 10 million+ planets under their control. And that's full "member" worlds.
2. "Hours" is for the fastest hyperdrives available. For a large transport, it's going to be less.
3. I'll also point out that Imperium Warp travel is invulnerable to Empire interdiction methods. That is to say, an Interdictor cruiser is not going to pull a ship out of the Warp. This is because Imperium vessels must go to the edge of a system to enter the Warp not due to gravitational influences, but due to the gribbly-energy-ness of the Warp.
It tends to be very bad for nearby planetary objects when you come out of the Warp in a planetary system. Note that some Inquisitorial vessels are exempt from this (in-system Warp jump=bad), due to far more advanced and higher-quality warp motors produced specifically for them by the Mechanicus.
Also note that the Eldar, Dark Eldar, and Necrons are also exempt from this (in-system Warp jump=bad), because none of them use the Warp for travel. Sadly for the Empire, none of them use a means which could be interdicted with an Interdictor cruiser, as the Webway has no relation to gravity, and Necron inertialess drive is a "press button=you're there" type of device.
Yeah, Necrons are ridiculous. But if you are going there, what ever happened to the races that built Centerpoint Station and the Maw?
As for a difficult conquest, It depends on how much the Empire wants intact. They could just BDZ everything they come across from orbit, then run away with their crazy fast hyperdrives.
AFAIK, there isn't any information on the species that built Centerpoint Station and the Maw, other than that they built said objects. Granted, these objects are quite powerful in their own right, but whether they were a massive undertaking or another day at said species' equivalent of an office, we don't know.
In contrast, we know quite well that current, Imperium-known Necron hardware are not their biggest&baddest toys. There's a record of a combined force of several Space Marine Chapters struggling to destroy a Necron vessel known only as the "World Engine", which is pretty much what it sounds like: a planet-sized tombworld, complete with shields and heavy armor.
It took ramming by a battle barge, one of the largest warships available to the Imperium at large (though more specifically, only the Astartes), to breach the shields in a localized position. Granted, that's something the Empire could easily do, but keep in mind that the battle barge rammed in order to deploy the strength of what was almost the entirety of an Astartes chapter, which then went through and completed the destruction of numerous shield generation systems, allowing for Exterminatus weapons to be brought to bear on the World Engine.
And Astartes are leagues above what the Empire can field.
TBH, the only reason I brought up the Necrons is to illustrate the point that SW doesn't mercilessly crush any and all opposition in a versus scenario.
Further, having the Empire simply BDZ everything the come across is counterproductive to the scenario. Granted, there wasn't one specified, but also keep in mind that if we assume it takes a day for one (1) ISD-II to complete a BDZ operation of a single planet, and we have 25,000 ISD-IIs at our disposal, and assume 10 million fully Imperium-controlled planets, then it would take 400 days to complete the operation. That's a bit more than a Terran-Standard year, and assumes that none of the ISD-IIs are lost.
And some of them will be lost to fleet actions, as there's quite a few planets that have substantial defensive weapons and ship garrisons.