I agree with Mike. The #5 1/2 is one of those planes that many see as a larger of a #5 – which is the plane I would select for a blade with an 8″ radius. Frankly, I do not see where it fits in.
It is too wide for a jack, which does better with a 2″ wide blade for thick shavings. It is too long for a smoother, which for wide panels one might better go with a shorter #4 1/2.
It is too short to be used as a jointer – one might as well go with a #6.
It has been made popular by David Charlesworth as a “super smoother”, but David does not dimension wood by hand – he simply smooths boards that were flattened on machinery.
I’d sharpening it up and use in on a shooting board, if you do not have a BU plane.
Regards from Perth
Derek