IIRC the plan for the N3's was a 25 knot speed, their armour would have been near Yamato levels too. She'd have been faster than the nelsons but not too fast, only 2 knots, which would have limited her utility later as she'd be slower than any canon threat like the Bismarck or anything in the Italian fleet. But it was also the fact that with her 18-inch guns and hella thick armour, if she did catch something, she'd kill it.