Fluff time: In the Sci-Fi movie world how would these matchups end up, who would vanquish whom details inside?

No one because they are all pretend.

1. Stormtroopers (not clone troopers) are conscripts, while Jem’Hadar are genetically engineered warrior race bred in cloning facilities. Jem’Hadar also have personal cloaks and superior weaponry.
The Jem’Hadar annihilate Stormtroopers.

2. Species 8472 have bested the Borg, and have the ability, with just a small number of bioships, to blow up entire planets. The entire dominion and their fleet only managed to perform conventional orbital bombardements, and thus mere surface damage.
Species 8472 defeats the Jem’Hadar.

3. The Borg assimilate, and adapt to, Jem’Hadar and their technology, cloning tech included, turning the Jem’Hadar’s strength against them.
The Borg easily defeat the Jem’Hadar

4. The Jem’Hadar, and by extension, the Dominion, have energy dampening weapons that can easily disable any Klingon Vessel. Plus their ability to cloak in ground combat and easily replenished numbers, makes this an easy win for the Jem’Hadar

5. Species 8472 will easily destroy the central worlds of the Galactic Empire and their ships, while poweful biological defences against technological, physical, chemical and biological attacks will ensure an easy victory against Storm Troopers on the ground.
Stormtroopers will be eaten alive by Species 8472.

6. see 1.

7. Stormtroopers lost against teddy bears armed with sticks. There is no way they will defeat Klingon Warriors.

8. Klingons get destroyed by Species 8472.

9. Klingons get assimilated by the Borg.

10. Jesus gets raped by all of them.

^ < sigh > it would have gotten a GA out of me which I hardly ever give but for that redacted last irrelevant and disrespectful comment.

What Loli said.

^ What Loli said.
Do you think he/she/it considered that the Jem’hadar has to get into a ground battle to maybe have superiority? I am not a Jem’hadar expert but I never seen them have equipment like speeders, At-At walkers, Imperial Star Cruisers or anything like the Death Star or their spoiler alert latest whole planet weapon, which if they had one operational they could bitch slap the Jem’ hadar before they could even dusk or sneeze….just an observation, but if they can engage the Stormtroopers (nonclone type) they may fair quite well, but I believe the Stormtroopers would have gave the Federation foot soldiers a run, and even they beat the Jam’hadar.

Of all the groups listed, the real power is in the Borg and species 8472. Even with the muddled storytelling in ST: Voyager, I think species 8472 would still come out on top.

Probably the only approximately fair matches on your list would be:

Species 8472 vs. the Borg
Klingons vs. the Jem’Hadar

Everything else is no contest, as @ragingloli said. I think, ship-wise, this is still true. And I still have trouble suspending disbelief that Death Stars can even travel. Surely, they’d wreak havoc with the gravity of the local star system and vice versa?

This is not “fluff” goes way beyond that, we’re entering nerd central right here, a rarified atmosphere where people can easily lose what’s left of their tiny minds.
So with that said, here’s my take, stormtroopers are little more than tap dancing gimps clad in plastic & offer, in terms of fighting prowess, exactly what you’d expect from that demographic.
As for the remaining combatants, all would have their arses roundly kicked by the munchkins, expertly coached by the loompah’s of oompah.

Storm troopers in all their advanced weaponry couldn’t take out an 18 year old boy whose only piloting experience was harassing desert animals on his go-kart.

They don’t have a snowball’s chance in hell against the Jem’Hadar.

Go munchkins, go munchkins, uh-huh…oh yeah!!