Of all of the fights on this list, this is the one that never fails to get my mind racing.
In many ways, Frank Shamrock was the prototype of the fighter that GSP has become: skilled in many areas, excellent on the ground, relentlessly committed to conditioning, etc.
At the height of his power, Shamrock could do it all: his striking was far better than most (and it was varied), his cardio seemed limitless, his ground game was consistently ranked among the best in the sport, and he always went for the finish. When you add to all of that the fact that he was perhaps the most explosive fighter in the sport, and you have the champion who defeated all comers in the UFC, finishing them all.
GSP is much like this, but he exists as a variation on a theme: he too is dedicated to conditioning, has a good striking game, and like Shamrock is a thinking mans fighter, implementing game plans built to play to his strengths while attacking the weaknesses of his opponents.
The differences between these two greats is found in their ground games: GSP is a fighter who possesses the best wrestling in the division and thus that is the basis for most of his offense, where as Frank Shamrock’s ground game was almost totally based around submissions.
So, who would win between these two men if we would have had the honor of seeing them face each other?
Shamrock enjoys a slight edge in the striking department, but it is very close. GSP is a very good striker, and he has a jab that is far better than Shamrock’s. They are both about dead even when it comes to how they employ leg kicks, save that GSP attacks the outside more than Shamrock, who loves to kick on the inside of an opponents legs, disrupting their balance.
But Shamrock had the better hands overall and he had the better defensive skills on the feet: his head movement was very good and he was a very capable counter puncher, and when he wanted to use his knees, he was devastating.
This is a fight that would only see a true answer to the question via a trilogy.
GSP would have the edge in raw power, takedowns and wrestling, which would see him work tirelessly from the top. Shamrock would have the edge in striking and submissions, constantly moving from the bottom and making GSP work more than anyone else to date and with Shamrocks eye for finishes and his explosiveness, GSP would be in the danger zone at all times, even from the top.
I see GSP winning one fight via a close decision, where as Shamrock wins another via submission.
As for the third fight, who honestly knows? But I would bet the bank that it would win fight of the year, hands down.