IMHO, you are concentrating on old metrics. Sailboat design has significantly evolved over the last 20 years. And there are a couple of key components that have changed in modern hull design. These are not just limited to production boats like Hunters, Catalinas or Bennies. You can find them in more expensive boats like Oysters and Hylas.
The most important of these is initial stability vs. overall (some times called secondary) stability. Essentially, more modern designs (wider beams carried further aft, fin keels and lighter displacement) have higher initial stability than classic designs (narrower beam, full or fullish keels and heavier displacement). But classic designs have higher overall stability. At first this looks like it hits the classic sailing forum argument of light cruiser/racer vs. heavy cruiser. But there is a little more to it.
Having a high initial stability and lower overall stability doesn't rule a boat out as a cruiser. Think about the extreme example of this, catamarans. Catamarans have a very high initial stability but the overall or secondary stability and righting motion is lower than the classic heavy cruiser. Yet there are plenty of examples of catamarans being cruised successfully and surviving storms at sea.
What the difference of initial stability vs. overall stability does tell you is how the boat likes to be sailed. Catamarans aren't sailed healed over at 20 degrees. And essentially the same is true of modern designs. They are sailed more flat footed. In my Catalina 310, I find that when I am healed over 15 degrees I start to loose speed. So with a modern design you need to learn when to reef, typically sooner than more classic designs to maintain speed, and other sail trim methods for depowering and flattening out your boat.
The problem with using some of these basic statistical measures is that often differences in design don't manifest themselves in these numbers. When you look at the overall length and beam the two Hunters look pretty similar. But the LWL on the 420 is 1.5 feet longer and when you look at the hull design the beam is carrier further aft. On the 42, the headsail carriers more sf but on the 420 the main carries more sf. None of this is accounted for when you only look at D/L ratio but it will all have an affect on the boat as a whole. Ted Brewer has a good primer on all of the boat statistics on his page (
http://www.tedbrewer.com/yachtdesign.html). By the way, he would consider both of these boats light cruiser/racers simply based on the D/L ratio.
And I would not take the word of some jerk on a forum (like me). I would do my own research on these things. Ted Brewer's page is a good place to start. Google will fill in the rest.
Good luck and fair winds,
Jesse
