yes i'm sure it is large, but it is nowhere near as large as UWS and Harvard so using those two universities is not a great idea.
and in saying that, those 'top universities' are
a) a matter of a panel of peoples opinion (which is valid, i'm sure but nonetheless very hard to be subjective)
b) as you get closer and closer to the top, its total wankfest as to who actually deserves number 1 or 2 or 3 etc. because i think they'd just be splitting hairs getting so close. its not like uni number 100 has toilets and university number 300 does not have toilets on campus. do some research into the top universities before assuming its a cut and dry ranking system. its like the top 100 in the state for uai, does number 100 a complete dumbass and number 1 a genius? not realy
c) its very hard to quantitatively measure how great a university is unless you strictly measure employment prospects, pay, etc. (Which isn't necessarily the best way to measure a university's quality) and even in saying that, its upto an individual to get a job or employed.
the only reason harvard, oxford, cambridge etc. get jobs so readily is because employers invite the graduates out to dinners! they offer them jobs, they dont make them work over summer for peanuts and _may_ offer them a position.
and also, by making a uni batshit insane hard to get into (lets set the issue of quality aside) chances are they will study their ass off to remain there and go well. its kinda like if you oppress someone they will either cave in our boune back and go better than they normally would.
the above explains why 1st and 2nd generation immigration people tend to own about 4 houses but drive a 1982 ford cortina