Significantly bigger than a Marine, as far as I've gathered;
'Talos regarded the vaguely humanoid shape as his sight resolved into an approximation of clarity. The Exalted wore the same relic armour so revered by the Atramentar (Terminator Armour) but... changed. Warped. Literally. Occasional flickers of warp lighting rippled across the surface of the armour. The witchlight gave off no illumination of its own.'
'The Exalted dragged itself closer to the table. A mild tremor shook through the chamber as the creature took a single step.'
'A portrait of too many fangs and acidic drool. Talos glared into his lord's black eyes, and the twisted face of a man he'd once admired.'
'The Exalted licked it's teeth. It still wore its armour for the most part, although the ceramite had long since become part of its altered flesh. The apothecarion was expansive, but the Exalted's nature forced it into an uncomfortable hunch to avoid scraping its horned helm across the ceiling... the Exalted stroked a taloned finger across a surgical table.'
'Its lips peeled back from its shark's teeth in a grin in didn't feel'
'Metal wrenched in protesting chorus with the harsh words. The Exalted's monstrous talon deformed the wall where the creature gripped too hard. With a grunt, it pulled its claw free.'
'The daemon heaved its exoskeletal bulk out of the throne, armour joints creaking'
'Vandred gestured to the hololithic, forcing himself not to be distracted by the clawed monstrosity that his right hand had become.'
That's all the description I can find from a skim through the books.
I thank you for the that answer!!