Very true, and I wasn't really comparing keepers ability, just mentioning my favourites.
I will say though, the Rennie held his place in the team with a couple of different managers despite being part time when the rest of the squad were full time, and McRae played outfield as well as in goals, so I suspect, with absolutely no evidence to support my arguement, that McRae would have been a very good "modern" goalie as he would be comfortable with the ball at his feet.
Your arguement about the lighter ball is valid, but the reverse is also true, could today's goaly cope with the physicality of sixties / seventies football when the keeper was fair game for the opposition forwards to barge, blooter or generally abuse.
Nostalgia just isn't what it used to be.