Take a look at the Justin fight for Khabib, all Justin did is back up (and supposedly won a round, not sure how though) GSP would just drive Khabib forward, take a double leg of use his strength to push Khabib against the fence, jab and not give in to the pressure. Not saying it would be a blow out either way but, GSP's jits, wrestling, striking and pressure are very hard to deal with, add a usually master gameplan to beat you. GSP is hard to bet against, age and injuries would be the biggest factors working against him. Would be such a fun fight, but the never endind discussion will probably give us more entertainment.