I saw a newscast a few years ago where they were talking about Mike tyson's punching power of 1800 lbs of force. Now we have to accept that GSP is far more powerful puncher than Mike Tyson.
Check out how weak and slow he punches the bag five times.
Well i think the reason why GSP punches harder than Tyson is due to GSP having access to better nutrition like Cell Tech and Pro Performance. Technology helps human beings reach higher unattainable goals than years ago. Tyson would still be a hard puncher in todays age, I would say.