I think it's impossible to compare golfers from different eras. Nicklaus had an incredible record, particularly with regard to performance in majors. It will be very tough for Tiger to equal Jack's record no matter how long he plays.
I think another factor for me is that for me, the competition was tougher for Jack, at least amongst elite players. Jack had the Big 3, himself, Gary Player and Arnold Palmer, then Tom Watson and many more.
Who has been Tiger's competition since he appeared on tour? A modern great... Phil?, Ernie?, Retief?, Vijay...? Puhleeze, none of those will be regarded alongside Player, Palmer and Watson.
What Tiger really needs to establish his greatness is a true challenger like Jack had... a great golfer for the ages. Until then he'll just be the best of a pretty mediocre lot IMHO.