There are PLENTY of reasons and ways to prove Might Guy has a set speed, before I even go into “infinte speed.”
1. Minato Namikaze moved so fast that it made Might Guy look slow, that alone is proof enough as if Might Giy had infinte speeds, Minato shouldn’t have even been able to see him especially since he has no dojutsu.
2. Kakashi was able to use Kamui to help assist Might Guy, once again, had Might Guy had infinite speeds, he wouldn’t even be able to see Gai, even the sharingan has its limits as been seen numerous times such as Sasuke fighting killer bee, unable to react and barely see Killer Bee’s movements. So infinite Gai should infintely above Kakashi(which he’s not).
3. A stronger Madara Uchiha shot out the Sage Art Light Fang which moves at only the speed of light, considering Naruto>Gai and Sasuke>Gai there is no plausible way Gai has infinite speeds.
Finally: Infinite Speeds is to instantly be anywhere or moving so fast time stops, since time continued and gai didn’t instantly kill madara, this has fully been debunked