Sprocket nuts !

Anyone got any opinions on changing the rear sprocket nuts, I assume the originals are steel, thinking of changing to aluminium nuts (see ebay ad below), ad says they are made of aircraft grade aluminium, manual recommends 59nM, should I still torque them to that figure?, any imput would be appreciated, thanks in advance  

http://www.ebay.co.uk/itm/Green-CNC-Rear-Sprocket-Nuts-Set-Fit-Kawasaki-Z1000-10-15-/321983659122?hash=item4af7b8bc72:g:lRsAAOSwFqJWoQzx

I'd say torque them the same and if they're not up to the job? they'll be the softer of the two metals and the nut's will be the ones that strip out, my BMW has Steel bolts into the aluminium wheel and the torque value is 60nM , vice versa of yours on the Z.

Thanks Sim