OK, I'm going to have to respond to this one. I've got a 28' or so aluminum cat with cabin forward and full house. It's a New Zealand design which my brother and I built over the course of a year of weekends and nights. It's powered with twin Honda 150's, three blade props. Reading the comments above, I'll comment:
Speed. Monos are faster. They've got less hull drag. So, if you're one of the gold chain guys, you'll never be happy unless you're talking about an asymmetrical racing hull and true speed...where cats rule. But if you want to run to Baker at 40 knots, and can stand the ride and fuel, look to Yellowfin, Contender or one of the excellent monos.
Efficiency. I've got a big 28' boat with full cabin, separate head and a wheel house that seats 4-6. It's got a good sized fishing cockpit. It's about to have in deck fish boxes when I get around to it. It holds 100 gallons of gas in two tanks. We cruise at 18-28 knots, depending, and average better than 3 mpg. Now, this is a fully planing hull. It is not a displacement or semi displacement like Glacier or WC, which typically get about half this mileage in real world but have a better headsea ride. But it's nice to be able to make two offshore runs on 100 gallons, so I'm happy with the compromise. It rides far, far better than the Grady sailfish, hydrosport, shamrock, privateer, aquasport, and others too far back to recall. Our top speed, with fuel and some pax is 40 knots, full to the pins and tweaked to the max.
Handling. I've never owned a high performance mono of this length but I expect they're easier to run. If you want the cat ride into the slop headed out, you can get it...leaving the 31 Bertrams and such far behind, but you're going to be doing some piloting. She'll launch off a direct head sea. True, the landing is without pounding, rather a solid sounding thump...but I don't like getting thumped either. So, when that 5-6 rears up among the 3's, you gotta hit her at some angle. That makes the hulls work really well together, and you breeze right through, but you got to have an eye on the sea. Heading back in, however, with our full planing hull, just shove the throttles forward and point her in the right direction and relax. Never, ever shown any tendancy to broach.
Beauty. This one really makes me want to puke, but if you're looking for a beautiful floating babe which you will want to polish, wax, stand back and admire the traditional lines and so forth...look elsewhere. I find lots to like about the seahandling and efficiency of my rig.
Strength. I'll be glad to engage any recreational fiberglass boat in a strength contest, winner claims salvage. Two years of hard running, never a failure of any sort.
Fishing. Biggest problem is all the mahi that want to hang out in the shade of the tunnel. She's reasonably comfortable at rest, especially compared to some deep v's I've owned. The motion is different, however, not a long period roll from side to side, but two quick short rolls per wave. Takes some getting used to, but overall preferable for me.
I'm seeing a change in the marine market coming, people are still going to fish but they're going to look twice at 600.00 fuel bills for a weekend. I think efficiency is going to displace top speed as a priority, more like the guys down under. With this in mind I feel like I've got as near perfect boat as I'm likely to ever see. Really, when you stop and think about it, there's no such thing as a fast boat, there's boats that are faster than other boats, but for speed you need wheels or wings.
Chuck