I assume most astartes fight using conventional knife fighting styles, but fight other astartes similarly to how knights in the ye olden ages would fight, mostly wrestling and grabbing to get at weak points to shove their knife into, ie their eyes.

Knights didn't have any wrist-mounted weapons to my knowledge so he'd have to adapt his fighting style. Though I'm not sure how strong an armored Spacemarine is, I'm damn sure a Predator can keep up with him.

Or it just doesn't bother and tries to get a cut into the back of a marine's knees. Play it fast and try to cut at openings in joints or shove it's wrist blades through the marines eye sockets. Marine's most likely win is getting a hold of a Yuatja and stabbing it it a critical area and try not to get blown apart by a personal bomb.

Not to mention that Elite Predators have access to a myriad of other weapons like the Combistick, the Netgun, and the Smart-Disc just to name a few.

I mean knights as in, two astartes slamming knives into each others armor doesn't do anything but put gouges into the armor, and only ever penetrates weakened armor. Going for joints and openings in armor like the neck or eyes was more effective.

I think the Smart-Disc in particular can go through Astartes armor, seeing as how it sliced through about 6 sides of beer and decapitated a man without losing a lick of speed.

Beer?

Beef

Ah. I doubt that it's enough to punch clean through the chest plate or the pauldrons. Enough to sever a hand or arm at the elbow, or into the neck and throat, But I doubt it would rip through a marine.

Or conversely, at the back of the marines leg would be enough to cripple a marine. The armor behind the knee isn't as thick.

They're tough enough to go through the armored bodies of several Combat Androids at once

Ceramite armor can survive rocket launchers. Cutting through ceramite is usually achieved at great constant applied physical force (Like a vice or a chainswords teeth constantly chipping flakes of armor away, or by tearing it asunder with a force field made of pure energy like with a power sword.) Or by great and excessive blunt force, like a thunder hammer or power fist or something way larger and heavier slamming into them. No matter how razor sharp a throwing disc is, cutting through hardened and advanced metal material often close to an inch thick isn't something I can picture it doing easily. The spear on the other hand, seems like a perfect answer. Small weapon profile, with a slender piercing blade would most likely be able to puncture ceramite armor over a slashing weapon.

Typically the blades of the Smart-Disc are covered in microscopic saw blades that spin, effectively making it a molecular chainsaw.

Then it would work if the predator held it against a marine, not so much throwing it and hoping it sticks.

It is sometimes used as a melee weapon but is primarily a thrown weapon

Though I'm pretty sure the Predator itself can break the Astartes' armor

something smells like toasted ham and cheese, so I thought I’d say hi Grim.

Hello

Short time no see

Likewise