Well he had gates, and could use all of them up to 8, something even Lee can't do. He took a long time to do it and train his body so he could.
Since he is a genin, we could compare him to Lee when he was a genin, but able to open 7 gates without dying. This would put him at a level above gaara and Sasuke at the time who I would consider to be at least chunin, nearing jounin level strength. I would say he is probably a mid-Jounin level ninja in strength with 7 gates open, for however long he can keep them open for.
8 gates open, he is obviously above kage level strength and speed.