One is made out of ductile iron, the other isn't.
Do they both weigh the same?
Many have said these premium planes to be too heavy......
Though being a no.5 1/2, and with sides actually square,
this might not be a terrible thing, and the greater area of the LN might make a
very small percentage difference (for one who's looking for problems)
I wouldn't be devastated if someone swapped my vintage Stanley 5 1/2 shooter for a LN version,
and could be a small bit less careful with it, having my shooting board often on the end of the bench.
Why do Clifton still make gray cast iron, and do they also offer ductile, perhaps if even for the block plane, it would be nice to know.
Lastly the choice may be the sharpening media you choose, L-N's A2 steel not being favourable with oilstones, and with such thick irons might not make finding something with say 01 or whatever favourable steel that will sharpen without glazing yer oil stone, (should that be your preference)
That's my 2 cents,
Tom