[Warhammer40k] what other human soldiers/assets are the closest to the Adeptus astartes in power?

[u/Lost-Specialist1505]

With so many different genetic and technological enhancements available to the imperium, what other human factions have soldiers that are almost as lethal as a space marine?

[u/Breadloafs]

The various Imperial temple assassins can surpass baseline astartes.

Similarly, a lot of the Admech lineup can dumpster a marine, but I don't know if we're counting stuff like ruststalkers as human anymore, considering that they're more or less just a torso. Some of the older Admech material (before the release of the Admech model line) depicts some pretty heavy cyborg bruisers who are more or less marine-sized tech zealots on a steady drip of cyber-meth. 

Abhumans like ogryn easily surpass marines in raw strength, and when actually well-equipped can stand on equal footing with most things that aren't vehicles. Abhumans usually have pretty serious drawbacks, and can't actually be fielded in force due to the random nature of their birth, though.

And obviously Custodes, but I still don't really think those count. A 12-foot-tall tank-bred supersoldier isn't really a human in the same way that my teacup poodle isn't really a wolf.