I'll just assume this is referring to Cell Arc Yamcha, given that's his peak as far as we know outside of filler.
Judging how strong he is compared to the other humans is difficult. Kuririn refers to him and Ten as two large Ki, yet even Raditz could be presented as an incredible Ki in the context of regular Earthlings. Kuririn didn't distinguish one as far above the other though, so you could cite them as comparable. Going to the absolute high-end of Yamcha being near Ten's level (of who I'd place around Sick Base Goku's level from him dodging #20's eye lasers in a similar timeframe), then I'd say Yamcha at best would be someone far stronger than a hypothetical SS2 Gotenks, yet still someone who Evil Boo could stomp at his full power. That said, he only gets past round 1.