As for the Strength amp, I think from what I've seen of Rex's personality, he's the exact kind of person who would piss Garou off in my opinion, not enough for a huge buff, but Garou would already be irritated, and with a slight, so after Rex begins to counter Garou's attacks, Garou would further be frustrated, this'd continue, and Rex would be trying to get Garou with the sword, which Garou is likely to avoid, there's no way, having his level of skill, that he's letting a giant ass sword anywhere near him, not without some form of plan on Rex's part. Garou doesn't usually begin using his Dusting attacks at first, so that wouldn't get adapted to until Garou gets pissed enough to throw literally everything he has at Rex, some of Garou's techniques would likely be adapted to, the fight'd continue, with Garou on the back foot, and there's enough reason to think that Garou would take some hits, which would likely be regenerated from rather quickly, as well as Vice Versa to Rex (Since I don't think Garou would try to dust Rex right off the bat, not until he's sufficiently angered), Garou at some point, would have his evolution kick in, with neither being able to really get the edge on each other due to their equal stats, and both of them having high levels of skill (I'm purposefully not using it as a decisive factor, since it's something I don't agree with, and I know the other side won't fold on), And he'd have a massive speed amp, at which he'd likely land quite a few impacts on Rex, which also, wouldn't kill Rex, eventually, Rex might create something to counter Garou's speed, since he has pretty haxy adaption, and would have to have taken numerous impacts, However, Garou still has his Vibrations, which you can bet, with not being able to Kill Rex sufficiently quick enough for his tastes, and due to his evolution slowly monsterizing him, he'd finally be pissed enough to start dusting things, the first to go, being Rex's adapted equipment, which would drop his speed adaption, from their, Garou blitzes and Dura Negates
You know who Im voting for with this little narrative