i would reckon that although the ae86 is supposed to be better as standard, i think that if you got a silvia and an 86 and modifeid them to the same levell of tune using similar or the same components i reckon the silvia would end up better. surely most of the silvias extra wieght is in its interior? i.ve had a couple of toyotas( a front wheel drive corolla gti 16v and a mk1 mr2) and both of thier interiors were very flimsy and lightwieght, whereas in my silvia its like having 2 velour armchairs and its all bolted together with cast iron!
of course i'm probably wrong cos i've never seen an ae86.