Aizen would almost have to be at least twice the strength of an average captain.
Aizen stopped Ichigos Bankai sword with 1 finger. Ichigo fought on par with Byakuya and Kenpachi with those abilities.
This was not an illusion like I previously thought becasue Ichigo was not under Aizens hypnosis.
Assuming Ichigo's strength with bankai at the time was on par with an average captain and Aizen stopped his sword attack with 1 finger I would say he's a beast and not just a liar.