Re: 45' + blue water cruiser
Plenty of discussion on that topic elsewhere on this forum.
Lead is heavier, so ballast can be smaller/more compact.. lead is more forgiving (softer) in a grounding situation but some say that can actually transfer more forces to hull structures.
Many of todays bulbed/torpedo keels couldn't be made purely of lead, lead lacks structural rigidity on its own. Usually they are steel/iron fins with lead bulbs attached.
Iron keels can be a PITA if not properly sealed.. each haulout is a rust scraping and repainting nightmare.. if properly sealed it's no different than lead in that regard as long as you don't compromise the membrane.
Keel bolts can be more easily changed/renewed in most iron keels, very difficult to do in lead keels as they are almost always "J" bolts cast into the keel when it's poured.
Personally I wouldn't let that be a deal breaker (esp with today's newer boats) but for many an iron keel would be.. (We've owned 5 boats so far over the past 30 years, 3 were iron, two lead)
1984 Fast/Nicholson 345 "FastForward"
".. there is much you could do at sea with common sense.. and very little you could do without it.."
Capt G E Ericson (from "The Cruel Sea" by Nicholas Monsarrat)