If you are trying to get an overview or comparison of various boats you could flip through the "Sail Calculator Pro", now at V3.54 http://tomdove.com/sailcalc/sailcalc.html It looks like it is being maintained so might have current information.

Comparing an Island Packet 27 to Hunter 27 (2005) shows the SA/D for the IP is actually higher than the Hunter. Looking at the numbers in a vacuum I'd say they would perform very similarly, maybe a slight edge to the IP. I'd also look at PHRF ratings to give an idea of how fast the boats are sailed. These ratings vary from one geographical location to the next but here is a link to PHRF NE http://www.phrfne.org/page/handicapping/base_handicaps

This shows a Hunter 27 at 219 and the Island Packet 27 at 234. I can't remember which Islander you had but the 28 is rated at 201. These are seconds per mile numbers so lower is faster. PHRF will generally give a better indicator of how fast a boat sails. The IP rating of 234 would be an indication of why they are sometimes referred to as Island Piglet. As you likely know from your own experiences, the longer the keel the better the boat tracks but the harder it is to maneuver.

Cruising sail boats tend to be a compromise. I lean a bit towards the sailing performance side so I like a fin keel and spade rudder but if you want a trade off between that and a full keel riding on rails feeling I'd go with a long keel (not deep, but a long chord) with a separate rudder. Having a skeg hung rudder is a big compromise that I find hard to justify but seems fairly popular. Maybe a balanced rudder on a skeg would be a good way to go, I just don't like barn door rudders.